Programming Notes for Mid-Year 2020
Computer
Science
9618
Huma Imad
P2 Computer Science 9618
Contents
What is an Algorithm? ..................................................................................................................... 5
What is the difference between a Pseudocode and a program flowchart? .............................................. 5
Precedence ........................................................................................................................................... 14
Control Structures ................................................................................................................................. 18
Formats of Control Structures ............................................................................................................ 18
Sequence ............................................................................................................................................... 18
Selection ............................................................................................................................................... 19

If _Then_ EndIf ......................................................................................................................... 19

Case Structure............................................................................................................................ 19
ITERATION ............................................................................................................................................. 31
Comparison between While, Repeat and For loop (Pseudocode) ........................................................... 36
Practice questions ................................................................................................................................. 39
Rogue value ................................................................................................................................... 40
'Menu driven program........................................................................................................................... 44
When to use
←
and
=........................................................................ 47
String operations ................................................................................................................................... 50
Random Number Generator .................................................................................................................. 68
Subroutines ........................................................................................................................................... 69
User Defined functions / Built-in functions ............................................................................................ 70
Differences ........................................................................................................................................ 70
Similarities ........................................................................................................................................ 70
Procedure Vs Function........................................................................................................................... 71
Passing parameters to subroutines .......................................................................................................... 76
Arguments/ Parameters .......................................................................................................................... 76
Different ways of Calling a Function ....................................................................................................... 81
Parameter passing by value/ by reference ......................................................................................... 84
Global Variables Vs Local Variables ................................................................................................ 90
Private Scope Vs Public Scope ........................................................................................................ 90
Arrays.................................................................................................................................................... 91
Arrays ................................................................................................................................................... 92
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1D Vs 2D Array .................................................................................................................................. 98
Single Search Result......................................................................................................................... 104
Multiple Search Result ..................................................................................................................... 104
Case insensitive search .................................................................................................................... 104
Case sensitive search ....................................................................................................................... 104
2D Array .............................................................................................................................................. 119
File Operations .................................................................................................................................... 124
File handling ........................................................................................................................................ 125
Example1- Write data on file ........................................................................................................... 126
Example 2a- Append data ................................................................................................................ 128
Example 2b-Append Data in a loop .................................................................................................. 128
Example 3 – Read data from file ...................................................................................................... 129
Using 2 files ..................................................................................................................................... 130
Rouge Value & File handling ............................................................................................................ 131
2 different file structures ................................................................................................................. 136
Searching in a Text File Vs Searching in an Array .............................................................................. 142
SUMMARY OF FORMATS ..................................................................................................................... 143
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Programming Basics
What is an Algorithm?
An algorithm is a series of instructions or steps for the solution of a problem.
What is the difference between a Pseudocode and a program flowchart?
An algorithm can be represented by a Pseudocode (Set of statements) or
a program flowchart (using symbols)
Pseudocodes
(English statements)
Converts to
Algorithm
(Program design)
Program flowchart
(graphical representation
of a solution)
Program code on
computer
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Data types
Pseudocode
STRING
DATE
CHAR
BOOLEAN
INTEGER
CURRENCY
REAL

Note
Variable average is always Real data type because it involves a divide operation.
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Pseudocode FORMATS
DECLARE <identifier> : <data type>
DECLARE Count : integer
CONSTANT <identifier> = <value>
CONSTANT Pi=3.14
CONSTANT Tax=10
<identifier> ← <value> or <expression>
Count ← 0
Count ← Count+1
INPUT <identifier>
INPUT Marks
OUTPUT <string>
OUTPUT “Hello”
OUTPUT <identifier(s)>
OUTPUT Marks
// this is a comment
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Built-in functions
Result ← 2^3
//^ represents exponent, result is 8
Num ← INT (3.5)
//INT is a built in function, returns only integer part of the decimal number, Num is 3
Num ← 5/2
//Normal division, answer is 2.5
Precedence
B
Brackets
E
Exponent
D
Divide and Multiply has the same level of precedence. Priority is
given to the operator on the left.
M
A
Add and subtract has the same level of precedence. Priority is given
to the operator on the left.
S
Solve Number = 2* 6 + 8 / 2 ^ 2
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Ans is 14
Declaration To reserve memory space according to array size and data type. Once the
memory is reserved there are junk values from previous programs in the memory.
Initialization To assign a valid starting value to an identifier. Now the junk value will be
replace by the initialization value. It is optional to initialize the variables that are being input.
It is mandatory to initialize variables that are being processed example count, total, max, min.
Statements (Pseudocodes)
Assignment
x ← 3 means the value 3 is written as the new value stored in the memory location labelled x,
x ← y means the value stored in the memory location labelled y is copied to the memory location
labelled x
Increment (Counting)
Variable ← Variable + 1
Example
count ← count+1
Statement used to increment variable by 2 (step size is 2)
Variable ← Variable + 2
Example
count ← count+2
(can be used for even or odd number list)
Statement used to increment variable by 3 (step size is 3)
Variable ← Variable + 3
Example
count ← count+3
(can be used for a table of 3)
**Similarly students should be able to write statements to increment any step size.
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Totaling
(step size is variable i.e. varying every time)
Variable1 ← Variable1 + Variable2
Example
Total ← Total + number
Subtraction Statements (examples)
Num ← Num -2
Total← Total - ((20/100)*Total)
…deduct 2 from a variable
…deduct 20% from a variable
Other examples of statements
NetTotal ← Total - ((20/100)*Total
…difference assigned to a new variable
Duration ← TimeOut – TimeIn
…difference of 2 other variables
NetTotal ← Total-Discount
…difference of 2 other variables
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INPUT and OUTPUT (Pseudocode)
INPUT Name
(No space in identifier; identifiers cannot start with a number)
OUTPUT "Your name is", Name
Prompt & Input (Pseudocode)
Method 1
Output “Enter Marks”
//Prompt
Input Marks
//Input
Method 2
Input “Enter Marks”, Marks
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Control Structures
There are 3 Control Structures
1. Sequence (One statement after another)
2. Selection (When you have choices and you must select one option)
3. Iteration (also called repetition ; when same thing needs to be done multiple times)
Formats of Control Structures
Sequence
Example:
Statement 1
Statement 2
Statement 3
PSEUDOCODE EXAMPLE
DECLARE A : INTEGER
DECLARE B: INTEGER
INPUT A
INPUT B
OUTPUT A+B
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Selection
When you have choices and you have to make a selection.
 If _Then_ EndIf
If is usually used when there are 2 choices to choose from (this is not a rule, only preferred).
 Case Structure
Case is used when there are more than 2 choices to choose from. Case gives a shorter and easier
code (this is not a rule, only preferred).
Pseudocode
Selection –IF
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Pseudocode
Selection- Case
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Pseudocode
THEN
On a new line
SEPARATE IF example
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NESTED IF example
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Pseudocode CASE
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Pseudocode CASE
DECLARE grade: CHAR
DECLARE mark: INTEGER
DECLARE choice: STRING
CASE of grade
CASE of mark
CASE of choice
‘A’: Output “Excellent”
90 to 100: Output “Excellent”
“Apple”: Output “Very Healthy”
‘B’: Output “good”
30 to 89: Output “good”
“Candies”: Output “unhealthy”
‘C’: Output “poor”
0 to 29: Output “poor”
“Meat”: Output “Healthy”
OTHERWISE output ”invalid
entry”
OTHERWISE output ”invalid
entry”
OTHERWISE output ”invalid
entry”
ENDCASE
ENDCASE
ENDCASE
*Note: Otherwise is optional; but It is good to use otherwise to validate input.
Variations of case structure
(Example channels)
(Example marks)
Case Channels of
Case Marks of
“Documentary”:
<50:
”Movies”:
50 to 80:
“Drama”:
>80:
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Multiple cases in one statement
CASE OF Speedometer of
CASE OF Grade
1,2,3,4 : speed←”slow”
‘A’, ‘B’: Output “ good result ”
5,6,7: speed← “Medium”
‘C’, ‘D’: Output “Average result”
8,9: speed ←”fast”
‘E’, ‘F’: Output “Poor result”
More than one statement can also be written for each case
Comparison between IF and CASE
Example: Enter grades of 8 students and output the corresponding remark according to the table
given. Also output the number of students who got A, B and C respectively.
Grade
Remark
A
Excellent
B
Good
C
poor
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P2 Computer Science 9618
//include declarations
count ←0
countA←0
Answer:
//include declarations
CountB←0
CountC←0
count ←0
WHILE count<8
countA←0
INPUT grade
CountB←0
Count←count+1
CountC←0
IF grade=’A’
WHILE count<8
INPUT grade
THEN
OUTPUT “Excellent”
Count←count+1
countA←countA+1
CASE of grade
‘A’:
Output “Excellent”
countA←countA+1
‘B’:
Output “good”
ELSE
If grade=’B’
THEN
OUTPUT “good”
countB←countB+1
‘C’:
countB←countB+1
Output “poor”
ELSE
countC←countC+1
IF grade =’C’
OTHERWISE OUTPUT ”invalid entry”
THEN
ENDCASE
Output “poor”
ENDWHILE
countC←countC+1
OUTPUT CountA, CountB,CountC
ENDIF
ENDIF
ENDIF
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OUTPUT CountA, CountB,CountC
P2 Computer Science 9618
Q. a) Input heights of 20 students using For loop. Output the corresponding remark using CASE
(Use Pseudocode). b) Rewrite the code using nested IF
Height
Remark
1.0 to 3.9
short
4.0 to 6.5
good
More than 6.5
Very Tall
//INCLUDE DECLARATIONS HERE
//INCLUDE DECLARATIONS HERE
FOR Count← 1 to 20
FOR Count← 1 to 20
INPUT height
INPUT height
CASE OF height
IF height>=1.0 AND height <= 3.9
1.0 to 3.9: Output “short”
4.0 to 6.5: Output “good”
> 6.5: Output “Very Tall”
OTHERWISE output ”invalid
entry”
THEN
OUTPUT “short”
ELSE
IF height>=4.0 AND height <= 6.5
THEN
OUTPUT “good”
ENDCASE
NEXT
ELSE
IF height > 6.5
THEN
OUTPUT “Very Tall”
ELSE
OUTPUT ”invalid entry”
END IF
END IF
END IF
ENDFOR
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CASE STRUCTURE
Q1.
Pseudocode
DECLARE Marks : Integer
INPUT Marks
CASE OF Marks
< 40 :OUTPUT("Grade is U")
40 TO 60 :OUTPUT("Grade is C")
61 TO
80 :OUTPUT("Grade is B")
81 TO 100 :OUTPUT("Grade is A")
OTHERWISE OUTPUT(“Invalid
Entry”)
ENDCASE
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Q2.
PSEUDODCODE
Easier to use the following syntax
40 TO 49
But the following is also acceptable
>= 40 and <50
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Flowchart CASE STRUCTURE
ITERATION
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Pseudocode
Iteration
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FOR LOOP with step size
DECLARE value : INTEGER
FOR value  10 To 0 Step -2
OUTPUT value
NEXT
DECLARE value : REAL
FOR value  10 To 0 Step -0.5
OUTPUT value
NEXT
DECLARE value : INTEGER
FOR value  0 To 10 Step 3
OUTPUT value
NEXTFOR
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Types of loops
For_Next loop


For is a count-controlled loop
Set number of repetitions
Repeat _Until Loop


Repeat…Until is a Post-Condition loop
In Repeat _Until loop must execute at least once.
As long as the condition is false, it keeps looping. If the condition never becomes true, it will result
in an infinite loop.
While _End While Loop

While ..…EndWhile is a Pre-condition Loop

In While _End while loop may never execute (if the condition is false in the first
iteration)
As long as the condition is true, it keeps looping. If the condition never becomes false, it will result
in an infinite loop.
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P2 Computer Science 9618
Comparison between While, Repeat and For loop (Pseudocode)
Example : Write pseudocode to input 5 numbers, find the total and output the sum.
DECLARE count :INTEGER
DECLARE count :INTEGER
DECLARE count :INTEGER
DECLARE total : INTEGER
DECLARE total : INTEGER
DECLARE total : INTEGER
DECLARE number :INTEGER
DECLARE number :INTEGER
DECLARE number :INTEGER
count←0
count←0
total←0
total←0
total←0
number←0
WHILE count<5
REPEAT
No need of
INPUT number
INPUT number
count ← count+1
count ← count+1
total ← total + number
total ← total + number
Count←count+1
FOR count ←1 TO 5
INPUT number
ENDWHILE
UNTIL count = 5
OUTPUT total
OUTPUT total
total ← total + number
ENDFOR count
OUTPUT total
ENDFOR count
Both are acceptable
ENDFOR
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Loop for 5 times. Multiple ways of writing the loop
----------------------------------------COUNT 0
REPEAT
COUNT COUNT+1
UNTIL COUNT>=5
----------------------------------------COUNT 0
REPEAT
COUNT COUNT+1
UNTIL COUNT=5
----------------------------------------COUNT 1
REPEAT
COUNT COUNT+1
UNTIL COUNT=6
----------------------------------------COUNT 0
REPEAT
COUNT COUNT+1
UNTIL COUNT>4
-----------------------------------------
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'Find Minimum & Maximum
DECLARE max, min, count, mark : INTEGER
max  0
min  100
mark  0
WHILE count < 6
OUTPUT "enter mark"
INPUT mark
count  count + 1
IF mark < min
THEN
min  mark
ENDIF
IF mark > max
THEN
max  mark
ENDIF
ENDWHILE
OUTPUT ("min is " & min)
OUTPUT("max is " & max)
Trace Table
Input values are 4, 3, 6, 9, 2, 1
count
mark
max
min
output
//Method 2 - min and max can be initialized with the first input
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Practice questions
Q1) Input ages of 5 students. Find and output the youngest student’s age (use for loop).
Q2) Input marks for 7 students (use while loop). Find and output


the average marks
total marks
Q3) Input names of 5 students
Find and output name of the last student.
Q4) Input rents of 8 houses. Find and output the
 lowest rent
 highest rent
 average rent
Q5)
 Prompt the user to enter how many students there are in a class.
 Input marks of all the students
 Output the total marks
Hint:
INPUT students
FOR count =1 to students
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Q6) Input heights of 8 students




Output total height
Maximum height
Minimum height
Average height
Q7) Input prices of 6 items. Use while loop.
 Find and output the total bill
 Find and output how many prices were greater than $100
 Find and output the percentage of items that were greater than $100
Q8) Input prices of 6 items .Find and output the total bill (use REPEAT LOOP)
Rogue value
is used to terminate the loop. This should be a value other than the possible valid inputs.
This is usually used when it is not specified how many times the loop should repeat.
We cannot use FOR loop in rouge value.
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Q. Input Numbers until -1 has been entered. Output the minimum number.
a) Using while loop
DECLARE Min, Number : INTEGER
Min100
INPUT Number
WHILE Number < > -1
IF Number < Min
THEN
Min  Number
ENDIF
One input before WHILE
and one input before
ENDWHILE so that rouge
value is not processed.
INPUT Number
ENDWHILE
OUTPUT ( “Min is ” & Min)
Note: While loop may not execute even once. Repeat loop will execute at least once.
(include prompts in these solutions)
b) Using REPEAT
DECLARE Min, Number : INTEGER
Min100
INPUT Number
REPEAT
IF Number < Min
THEN
Min  Number
ENDIF
INPUT Number
UNTIL NUMBER = -1
OUTPUT ( “Min is ” & Min)
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P2 Computer Science 9618
Practice Rogue value
Q1. Input grades of students until z has been entered. Count and output how many times A* has
been entered.
Q2. Input prices of items until -999 has been entered. Output the lowest price.
Q3. Input marks of students until a terminating value has been entered. Find and output the
average marks. Choose an appropriate rogue value.
Example 1: Input a word of any length terminated by a rogue value “@”. Output the length
of the word. Pseudocode.
Ans.
//include declarations
length ← 0
char ← “ ”
INPUT char
WHILE char < > ‘@’
length ← length +1
Input char has to be
placed at the bottom
of the loop
INPUT char
ENDWHILE
OUTPUT length
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Case & Rogue value application
Q1. A shop sells books, maps and magazines. Each item is identified by a unique 4 – digit code.
All books have a code starting with a 1, all maps have a code starting with a 2 and all magazines
have a code beginning with a 3. The code 9999 is used to end the program. Write an algorithm
using pseudocode which input the codes for all items in stock and outputs the number of books,
maps and magazine in stock. Include any validation checks necessary.
(NOTE: A 4-digit code implies all books have a code lying between 1000
and 1999, all maps have a code lying between 2000 and 2999 and all
magazines a code lying between 3000 and 3999. Anything outside this range is an error)
Ans:
//include declarations
Books←0
maps←0
magazines←0
Input code
While code < > 9999 Do
CASE OF code
1000 to 1999: Books←Books+1
2000 to 2999: Maps←Maps+1
3000 to 3999: Magazines←Magazines+1
OTHERWISE OUTPUT “Invalid Entry”
ENDCASE
Input code
End while
OUTPUT Books, Maps, Magazines
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Iteration using rouge value
'Menu driven program
PROCEDURE multiply(x : INTEGER, y : INTEGER)
OUTPUT(x * y)
ENDPROCEDURE
PROCEDURE divide(x : INTEGER, y : INTEGER)
OUTPUT(x / y)
ENDPROCEDURE
PROCEDURE add(x : INTEGER, y : INTEGER)
OUTPUT (x + y)
ENDPROCEDURE
PROCEDURE subtract(x : INTEGER, y : INTEGER)
OUTPUT (x - y)
ENDPROCEDURE
PROCEDURE Main()
DECLARE choice : CHAR
REPEAT
OUTPUT("Enter M for Multiplication, D for Division")
OUTPUT("S for subtraction, A for Addition ")
INPUT choice
Case OF choice
‘M’:
CALL multiply(5, 3)
‘A’:
CALL add(5, 3)
‘D’:
CALL divide(5, 3)
‘S’:
CALL subtract(5, 3)
OTHERWISE
OUTPUT "invalid entry"
ENDCASE
OUTPUT "do you want to continue, Y/N"
INPUT choice
Until choice = ‘N’
ENDPROCEDURE
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Nested structures Pseudocode
NOTE:
ELSE IF on the same line should be avoided.
Nested IF
IF ….
IF…..
…………………..
END IF
END IF
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VB code
Nested For
FOR ROW= 1 TO 5
FOR COL= 1 TO 8
…………………
NEXT COL
NEXT ROW
Nested Loop
WHILE COUNT <4
Do
………………………….
LOOP UNTIL TEMP < 0
END WHILE
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Pseudocode
Note: It is compulsory to initialize counters, totals, min and max.
When to use
←
and
=
= is called a Relational operator
← is called an Assignment operator
= is used to check equality
In conditions we use =
Examples
 IF Num=0
 While Found= False…..
Repeat
….
 Until Found=True
← is used for Assignment
When we want to assign a value, we use ←
Num←0
Found←True
Min←100
Max←Num
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In pseudocodes
count←5
statement is correct
If count←5
condition is incorrect
If count=5 correct
If count←5 incorrect
= is known as a relational operator
← is known as an assignment operator
Assignment arrow cannot be used in a condition.
IF condition
WHILE condition
UNTIL condition
A condition always evaluates to TRUE/FALSE.
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ASCII Character Codes (0 through 127)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
(backspace)
(tab)
(line feed)
N/A
N/A
(carriage
return)
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Teacher : Huma Imad
32
33
34
35
36
37
38
39
40
41
42
43
44
45
[space]
!
"
#
$
%
&
'
(
)
*
+
,
-
64
65
66
67
68
69
70
71
72
73
74
75
76
77
@
A
B
C
D
E
F
G
H
I
J
K
L
M
96
97
98
99
100
101
102
103
104
105
106
107
108
109
`
a
b
c
d
e
f
g
h
i
j
k
l
m
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
.
/
0
1
2
3
4
5
6
7
8
9
:
;
<
=
>
?
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
[
\
]
^
_
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
n
o
p
q
r
s
t
u
v
w
x
y
z
{
|
}
~
N/A
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String operations
EXAMPLE : SIGN UP ACCOUNTS
First Name Ali
LastName Sarim
SUGGESTED USER IDs are as follows
AliSarim
SarimA
Ali.S
Ali.Sa
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String operations
School Time
Extract from left, right or mid
4321
Evaluate the following
LEFT("School Time", 3)
RIGHT("School Time", 4)
MID("School", 4,3)
MID (STRING, starting position, how many characters to extract)
MID("School", 4,3)
"C" & MID("School", 4,3)
TO_UPPER("temp")
TO_LOWER("CaMeL CaSe")
Concatenation
Joining two strings
& + operators are used for
concatenation
//Prefer using & instead of +
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String operations
Page 260 text book
'Extract from left , right or mid
DECLARE str1 : STRING
str1  "Pakistan"
OUTPUT(LEFT(str1, 3))
OUTPUT (RIGHT(str1, 4))
OUTPUT (MID(str1, 2, 5))
OUTPUT (LEFT("hello", 4))
OUTPUT (RIGHT("Cat", 2))
OUTPUT (MID(LEFT("Karachi", 5), 2, 3))
OUTPUT ((MID(LEFT("Karachi", 5), 2, 3)) & "five")
OUTPUT (MID("wi fi", 2, 3))
OUTPUT (TO_UPPER(str1))
OUTPUT (TO_LOWER(str1))
OUTPUT (CHR(65))
OUTPUT (CHR(68))
DECLARE str1,str2 :STRING
INPUT str1
str2  Left(str1, 3))
TO_UPPER and TO_LOWER are used to convert to
STRINGS TO uppercase and lowercase
str2 TO_UPPER(str1)
str2  TO_LOWER(str1)
LCASE and UCASE are used to convert to
CHARACTER DATA TYPE TO uppercase and lowercase
DECLARE LETTER1, LETTER2 : CHAR
INPUT LETTER1
LETTER2  LCASE(LETTER1)
LETTER2  UCASE(LETTER1)
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//to print alphabets
DECLARE count : Integer
For count  65 To 90
OUTPUT(CHR(count))
ENDFOR
Integer data type result
DECLARE str2 : STRING
Str2 "Karachi City"
OUTPUT(LENGTH(str2))
// 12- LENGTH OF THE STRING IS DISPLAYED.
//CONSIDER SPACE AS A VALID CHARACTER
OUTPUT(ASC(str2))
// ASCII VALUE OF THE LEFT MOST CHARACTER IS DISPLAYED
9608/21/M/J/16
Answer
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Q1. Write a Procedure DISPLAY ( ) that takes EmployeeCode as a string parameter. It extracts and
outputs the ID, Department and Name. EmployeeCode follows the following format:



3 digits of ID
4 characters of Department
Name of variable length
<ID><Department><Name>
Example 876ACCTSamad
Answer
PROCEDURE DISPLAY(EmployeeCode : STRING)
DECLARE ID : STRING
DECLARE Department : STRING
DECLARE Name : STRING
ID  LEFT(EmployeeCode, 3)
Department  MID(EmployeeCode, 4, 4)
Name  RIGHT(EmployeeCode, LENGTH(EmployeeCode) - 7)
OUTPUT ID
OUTPUT Department
OUTPUT Name
ENDPROCEDURE
(B) Write the corresponding call
CALL DISPLAY("876ACCTHina")
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Extract each character from a string
DECLARE ThisString :STRING
DECLARE ThisChar : CHAR
DECLARE count : INTEGER
ThisString  "hello"
'Method 1 (commonly used IN MARKING KEYS)
For count  1 To LENGTH(ThisString)
ThisChar = MID(ThisString, count, 1)
OUTPUT ThisChar
Next
'Method 2 ( NOT common)
//Count starts with 1 in Pseudocode. Works like an array of characters.
For count = 1 To Len(ThisString)
ThisChar = ThisString(count)
Console.WriteLine(ThisChar)
Next
Output would be
h
e
l
l
o
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Validation to check if ThisChar is a digit
If ThisChar >= ‘0’ And ThisChar <= ‘9’
Validation to check if ThisChar is a lower case letter
If ThisChar >= ‘a’ And ThisChar <= ‘z’
Validation to check if ThisChar is an upper case letter
If ThisChar >= ‘A’ And ThisChar <= ‘Z’
Q How many digits are there in ThisString?
DECLARE ThisString : STRING
DECLARE ThisChar : CHAR
DECLARE counter : INTEGER
DECLARE count : INTEGER
ThisString  "hello369"
counter  0
FOR count  1 To LENGTH(ThisString)
ThisChar  Mid(ThisString, count, 1)
IF ThisChar >= ‘0’ And ThisChar <= ‘9’
THEN
counter = counter + 1
ENDIF
ENDFOR
OUTPUT("number of digits " & counter)
Practice question
Write a procedure Validate( ) that takes ThisString as a parameter. It counts and outputs
the number of digits, lower case and upper case characters.
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Pseudocode_Strings
9608/21/M/J/17
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Past Paper Question
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FUNCTION ValidatePassword ( Pass : STRING) RETURNS BOOLEAN
DECLARE Count, CountD, CountU, CountL, Other : INTEGER
DECLARE ThisChar : Char
DECLARE Result : BOOLEAN
CountU 0
CountL  0
CountD 0
Other  0
FOR Count 1 TO LENGTH ( Pass)
ThisChar MID(Pass, Count,1)
IF ThisChar > = ‘0’ AND ThisChar<= ‘9’
THEN
CountD CountD+1
ELSE
IF ThisChar > = ‘a’ AND ThisChar<= ‘z’
THEN
CountL CountL+1
ELSE
IF ThisChar > = ‘A’ AND ThisChar<= ‘Z’
THEN
CountU CountU+1
ELSE
Other Other + 1
ENDIF
ENDIF
ENDIF
ENDFOR
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continued…
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IF CountD >= 3 AND CountL >=2 AND CountU>=2 AND Other=0
THEN
Result  TRUE
ELSE
Result  FALSE
ENDIF
RETURN Result
ENDFUNCTION
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Teacher : Huma Imad
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9608/22/M/J/17
Errors in the marking key are as follows:




LEN should be written as LENGTH built in function
ValidateRegistration  TRUE should not be at the top of the code.
IF NextChar <’A’ AND NextChar >’Z’ should be IF NextChar <’A’ OR NextChar >’Z’
IF NextChar <’0’ AND NextChar >’9’ should be IF NextChar <’0’ OR NextChar >’9’
Answer
FUNCTION ValidateRegistration ( Registration : STRING) RETURNS BOOLEAN
DECLARE L, UCount, NumCount, n : INTEGER
DECLARE NextCHar : CHAR
DECLARE Result : BOOLEAN
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Result TRUE
L  LENGTH (Registration)
IF L <6 OR L > 9
THEN
Result FALSE
ELSE
FOR n 1 to 3
NextChar  MID (Registration, n, 1)
IF NextChar <’A’ OR NextChar >’Z’
THEN
Result  FALSE
ENDIF
ENDFOR
FOR n 4 to 5
NextChar  MID (Registration, n, 1)
IF NextChar <’0’ OR NextChar >’9’
THEN
Result  FALSE
ENDIF
ENDFOR
FOR n 6 to LENGTH(Registration)
NextChar MID (Registration, n ,1
IF NextChar <’A’ OR NextChar> ‘Z’
THEN
Result FALSE
ENDIF
ENDFOR
ENDIF
RETURN Result
ENDFUNCTION
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ISNUM is a built-in function that returns TRUE if the argument is numeric otherwise returns FALSE.
Example
Str1  ”87534”
IF ISNUM(Str1)
THEN
OUTPUT “The string consists of digits only”
ENDIF
NOTE:
Str2  “7@GF”
IF Str2 = TO_UPPER (Str2)
Cannot be used to validate if the string is in uppercase or not because it will not be able to identify
digits and symbols.
Practice Questions
9608/22/M/J/17 Q3. Fill in the blanks
Q6 9608/21/M/J/16 Trace table
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SPECIMEN INSERT P2
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Pg. 261 text book
DECLARE num :INTEGER
Truncating numbers
Instead of rounding, sometimes we just want the whole number part of a real number.
This is known as 'truncation'.
num  INT (76.55)
// 76
Converting a string to a number
Sometimes a whole number may be held as a string. To use such a number in a calculation,
we first need to convert it to an integer. For example, these functions return the integer value
5 from the string “5”. Works for both integer and real data type.
num  STRING_TO_NUM (“5.95”)
//5.95
Date and Time data type
DECLARE MyDate :DATE
MyDate  #12/05/2020#
OUTPUT
Page 246 text book
In pseudocode, we can indicate whether a new line should be output at the end by a comment at the
end of the statement.
OUTPUT (“Hello”)
// newline
Hello
OUTPUT (“World”)
World
OUTPUT(“Hello”)
//no new line
HelloWorld
OUTPUT(“World”)
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Random Number Generator
RANDOMBETWEEN(min,max)
// generates a random integer between the integers min and max (inclusive)
Q. Generate 10 random numbers between 1 and 5
Num ← RANDOMBETWEEN (1,5)
//Note 1 and 5 are both inclusive
RND( )
// Always generates a random real number between 0 and 1.
Num← RND( )
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Subroutines
9608/22/M/J/19
2 (a) (i) Procedures and functions are examples of subroutines.
State a reason for using subroutines in the construction of an algorithm.
...........................................................................................................................................
..................................................................................................................................... [1]
(ii) Give three advantages of using subroutines in a program.
1 ........................................................................................................................................
...........................................................................................................................................
2 ........................................................................................................................................
...........................................................................................................................................
3 ........................................................................................................................................
.......................................................................................................................................[3]
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Subroutines/ Modularization
Definition
Programs are usually built up from small, self contained blocks of code called subroutines,
subprograms, procedures or modules.
It makes it easy for the programmer to write, test and debug code using modular approach.
Subroutines are of 2 types: functions and procedures
Predefined functions and procedures
Set of built-in subroutines that perform standard functions in a programming language
example MOD, INT.
Library routines
A LIBRARY ROUTINE is a set of programming instructions for a given task that is
already available for use. It is pre-tested and usually performs a task that is frequently
required. For example, the task ‘get time’ in the checking-for-the-alarm-time algorithm
would probably be readily available as a library routine.
Benefits of predefined functions/procedures or library routines:

results in reusable codes

A lot of programmer’s time is saved

Already tested and debugged
User Defined functions / Built-in functions
Differences
• Built-in functions are made available by the programming language / already in the
system
• Built-in functions are ready made and tested
• User-defined functions can be modified // built-in cannot be modified
• User defined functions can be designed to meet the user's requirements
• User-defined functions can only be used in that program / module
Similarities
• They have an identifier name
• They return a value
• They have none, one or more arguments
• Both perform a specific task
• Both represent re-usable code
• Both are 'called'
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Procedure Vs Function
Page 262 ; 265
Subroutines are of 2 types- Procedure or Function
Procedure does not return values
Function returns exactly one value
Procedure
Function
1 PROCEDURE Add(num1 : Integer, num2 :
1
Integer)
FUNCTION Add(num1 : Integer, num2 : Integer) RETURNS
Integer
2
DECLARE Result :INTEGER
2
DECLARE Result :INTEGER
3
Result←num1+num2
3
Result←num1+num2
4
OUTPUT Result
4
OUTPUT Result
5
END PROCEDURE
5
RETURN Result
6
END FUNCTION
‘Call to a procedure
‘call to a Function
Call Add(4,7)
Answer←Add(4,7)
Call Add(num1, num2)
Answer←Add(num1,num2)
Call Add(x,y)
OUTPUT (Add(4,7))
*changes are highlighted
NOTE
Line #1
 In procedure declaration keyword is PROCEDURE
 in function declaration keyword is FUNCTION
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 In procedure no return data type
 In function mention the return data type
Line # 5
 Procedure - No need of RETURN statement
 Function- RETURN Statement is required
 ENDPROCEDURE
 ENDFUNCTION
Subroutine Call
 Procedure- Use Keyword CALL
 Function- NO need of CALL ( output the returned value, assign it to a variable or use any other
suitable method).
Practice Questions
9608/21/M/J/18
9608/22/M/J/19
A procedure, CountLines(), is being written to count the number of lines in a text file. The
procedure will:
• take a filename as a string parameter
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Classwork
Write subroutine headers for the following
1.Function TEST takes a parameter MyCharacter of type char. it returns TRUE/FALSE.
2. Procedure PumpIN( ) that pumps in water in a swimming pool.
3. A subroutine Calculate( ) that returns the integer RESULT.
It takes three integer coordinates as parameter x, y and z.
Alternative method of returning a value
FunctionName  ValueToReturn
Instead of
RETURN ValueToReturn
FUNCTION Add(num1 : Integer, num2 : Integer) RETURNS
FUNCTION Add(num1 : Integer, num2 : Integer) RETURNS
INTEGER
INTEGER
DECLARE Result :INTEGER
DECLARE Result :INTEGER
Result←num1+num2
Result←num1+num2
OUTPUT Result
OUTPUT Result
RETURN Result
Add  Result
END FUNCTION
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END FUNCTION
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Procedure
Pseudocode
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Function(returns exactly one value)
Pseudocode
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Passing parameters to subroutines
Page 267 text book
Subroutine Interface: The parameters being passed between the subroutine and the calling
program.



Order of the parameters must be the same as the order of the arguments.
Arguments and the corresponding parameters must have the same data types.
The number of arguments sent must match with the number of parameters.
Arguments/ Parameters
When the main program calls a subroutine, the values being passed to the subroutine are
called arguments. In the subroutine the values are called parameters.
PROCEDURE Add (num1 : INTEGER, num2 : INTEGER)
// num1, num2 are parameter in the subroutine header
…….
ENDPROCEDURE
Corresponding call in another subroutine would be
CALL Add(x,y)
//x, y are arguments in the call
NOTE
x corresponds to num1 and y corresponds to num2.
Arguments and parameters must correspond to each other in terms of data types. Number of
arguments sent must be equal to number of parameters received.
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Errors
CALL Add( 3, “56”)
CALL Add( ‘a’, 45)
Data type of argument does not match with data type of parameters
[Extension: It is Runtime error]
CALL Add (45, 3, 78)
Number of arguments are not matching with number of parameters.
[Extension : It is a Syntax Error.]
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Q5. The company wants a program to output the total monthly sales for one of the
selected websites.
The programmer codes a function with the following function header:
FUNCTION MonthlyWebSiteSales(ThisMonth : INTEGER, ThisSite : CHAR) RETURNS
INTEGER
The function returns the total number of bicycles sold for the given month and website.
The function will use the following:
(i) Give the number of parameters of this function . ..............................................[1]
(ii) Some of the following function calls may be invalid.
Mark each call with:
• a tick (✓), for a valid call
• a cross (✗), for an invalid call
For any function calls which are invalid, explain why.
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Teacher : Huma Imad
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Q. A string-handling function has been developed.
a)
Label parts of the following function header
PUBLIC FUNCTION SSM(String1: STRING, String2 : STRING) RETURNS INTEGER
a
b
c
d
e
a____scope of function______
b___identifier, function name__
c__________paramete1_____
d_____data type of parameter1
e_________return data type
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Calling a Procedure (There is a single way of calling a procedure)
PROCEDURE MyProc( Para : INTEGER)
… …
ENDPROCEDURE
CALL MyProc( Num )
CALL MyProc(45)
FUNCTION MyNum ( Para: INTEGER) RETURNS INTEGER
…..
ENDFUNCTION
Different ways of Calling a Function
Function call is substituted by the value returned.
DECLARE Result : INTEGER
Result  MyNum( 23)
//Assigning the return value to a variable
OUTPUT (MyNum( 78))
//outputting the return value
IF MyNum(45) >90
// using return value in a condition
Result  7 + MyNum(5)
// use in a formula
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5 DATA SOURCES
Example: Output the double of Num. Value of Num can be received through 5 sources in our code.
1.USER INPUT
PROCEDURE DOUBLE()
DECLARE Num :INTEGER
OUTPUT “Enter number”
INPUT Num
OUTPUT Num*2
END PROCEDURE
2. Hardcode
PROCEDURE DOUBLE()
DECLARE Num :INTEGER
Num= 5
OUTPUT Num*2
END PROCEDURE
3. Global variable
//Some value has been set by other subroutines
DECLARE Num :INTEGER
PROCEDURE DOUBLE()
OUTPUT Num*2
END PROCEDURE
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4. Parameter passing
//Procedure is receiving the value of Num as a parameter
PROCEDURE DOUBLE( Num : INTEGER)
OUTPUT Num*2
END PROCEDURE
5. Read Value from a TEXT FILE
PROCEDURE DOUBLE()
DECLARE Num :INTEGER
DECLARE Data : STRING
OPENFILE (“TEST.txt” FOR READ)
READFILE (“TEST.txt” , Data)
Num← STRING_To_NUM(Data)
OUTPUT Num*2
CLOSEFILE(“TEST.txt”)
END PROCEDURE
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Parameter passing by value/ by reference
_________________________________________________________________________
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Text book page 269
Definition
By value:
– A copy of the variable itself is passed.
– leaving the variable in the calling program unaffected
By reference:
_The address of the variable is passed.
– Original value in the calling program is also changed when parameter
changed in called module.
According to CAIE outline: If the method for passing parameters is not specified, passing
by value is assumed.
Note that array arguments and user-defined type arguments should not be passed BYVAL
(because of their large size).
Also, using BYVAL or BYREF doesn't have any effect when the argument is a literal
constant--only when it's a variable.
Protection. In choosing between the two passing mechanisms, the most important criterion
is the exposure of calling variables to change.
The advantage of passing an argument ByRef:
 it eliminates the overhead of copying large amounts of data e.g. array
 is that the procedure can return a value to the calling code through that argument.
DISADVANTAGE OF by reference:
Weak security because procedure can modify the caller’s data at will, possibly changing
that data.
The advantage of passing an argument BYVAL
is that it protects a variable from being changed by the procedure.
Disadvantage of BYVAL:
Call by value is bad for performance if data being passed is large because making a copy of
that data takes time and consumes memory.
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Parameter Passing (pseudocodes)
To specify whether a parameter is passed by value or by reference, the keywords BYVALUE and BYREF
precede the parameter in the definition of the procedure. If there are several parameters, they should
all be passed by the same method and the BYVALUE or BYREF keyword need not be repeated.
If the method for passing parameters is not specified, passing by value is assumed.
If parameters are passed by reference (as in the above example), when the procedure is called an
identifier for a variable of the correct data type must be given (rather than any expression which
evaluates to a value of the correct type). A reference (address) to that variable is passed to the
procedure when it is called and if the value is changed in the procedure, this change is reflected in the
variable which was passed into it, after the procedure has terminated.
In principle, parameters can also be passed by value or by reference to functions and will operate in a
similar way. However, it should be considered bad practice to pass parameters by reference to a
function and this should be avoided. Functions should have no other side effect on the program other
than to return the designated value.
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BYVALUE
Consider the following program
PROCEDURE Test(BYVALUE x : INTEGER)
x  x + 1
OUTPUT(“x is ” & x)
ENDPROCEDURE
PROCEDURE LESSON( )
DECLARE a : Integer
a  2
CALL Test(a)
OUTPUT(“a is ” & a)
ENDPROCEDURE
OUTPUT IS
x is 3
a is 2
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BYREF
Consider the following program
PROCEDURE Test(BYREF y :INTEGER)
y  y + 1
OUTPUT(“y is ” & y)
ENDPROCEDURE
PROCEDURE LESSON( )
DECLARE b : Integer
b  3
CALL Test(b)
OUTPUT(“b is ” & b)
ENDPROCEDURE
OUTPUT IS
y is 4
b is 4
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Consider the following program
PROCEDURE Test(BYVAL x : INTEGER, BYREF y :INTEGER)
x  x + 1
y  y + 1
OUTPUT(“x is ” & x)
OUTPUT(“y is ” & y)
ENDPROCEDURE
PROCEDURE LESSON( )
DECLARE a : Integer
DECLARE b : Integer
a  2
b  3
CALL Test(a, b)
OUTPUT(“a is ” & a)
OUTPUT(“b is ” & b)
ENDPROCEDURE
OUTPUT IS
x is 3
y is 4
a is 2
b is 4
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SCOPE of a variable
Global Variables Vs Local Variables
Page 206, 266 text book
Global variables have global scope. They can be accessed from any subroutine. It is not a good
programming practice because data is insecure; any subroutine can change the global variable.
Global variables are written at the top of the code.
Local variables have local scope and they cannot be accessed from outside the current
subroutine. Data is more secure. They are accessible only within the module in which they are
declared.
Scope of a subroutine
Private Scope Vs Public Scope
Public scope of a subroutine means that it can be accessed from any module.
Private scope means that it can only be accessed from current module.
Example
PRIVATE FUNCTION TEST (Num: INTEGER)
PUBLIC FUNCTION TEST (Num: INTEGER)
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Arrays
1D Array page 212 text book
2D Array page 218 text book
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Arrays

Array is a data structure.

It is a set of continuous storage locations.

One dimensional array is a linear list.

All the elements in the array are of the same data type.

A two dimensional array or double dimensional array is known as a table with
rows and columns.

Index may start with 0 or 1
Explanation: In this example
Array name: Prices
Array size: 5
Index: 1 to 5
Array Data type: Real or currency
Lower
Bound
Upper
Bound
1
46.87
2
21.50
3
43.00
4
67.00
5
24.00
Teacher : Huma Imad
Array
element
Index/
subscript
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Finding total without array
Example : Write a pseudocode to input 5 prices. Find and output the average price.
DECLARE Total : CURRENCY
DECLARE Average : CURRENCY
DECLARE Prices: CURRENCY
DECLARE count : INTEGER
Total←0
Average←0
50
For count←1 to 5
Input Prices
Total←Total + Prices
ENDFOR
Average←Total/5
OUTPUT “Average is” , Average
Teacher : Huma Imad
Variable Prices
Each new value overwrites
the previous value
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Finding total with array
Example : Write a pseudocode to input 5 prices using an array Prices. Find and output the
average price.
DECLARE Prices: ARRAY [1: 5] OF CURRENCY
DECLARE Total : CURRENCY
50
DECLARE Average : CURRENCY
DECLARE count : INTEGER
Total←0
Average←0
For count←1 to 5
Input Prices[count]
20.5
37.9
60
25.3
Total←Total + Prices[count]
ENDFOR
Average←Total/5
OUTPUT “Average is” , Average
Array Prices
Values are stored in a list.
Values are not overwritten.
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Q. Input 1000 numbers in an Array using



For
While
Repeat
Pseudocode Syntax
DECLARE Num: ARRAY [1:1000] OF INTEGER
DECLARE count : INTEGER
For
count← 1 to 1000
Input Num[count]
ENDFOR
DECLARE Num: ARRAY [1:1000] OF INTEGER
DECLARE count : INTEGER
count←1
Repeat
Input Num[count]
count←count+1
Until count>1000
DECLARE Num: ARRAY [1:1000] OF INTEGER
DECLARE count : INTEGER
count←1
While count < =1000
Input Num[count]
count←count+1
ENDWHILE
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Q. Write statement to output the 7th number
Output Num[7]
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Initialization values can be different for different questions
Name[Index] ← “ ”
(or Null)
Marks [Index] ← -1 ( or 0)
CheckerBoard [Index] ← “ ”
Number[Index] ← 0
Product[Index] ← 1
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1D Vs 2D Array
Pseudocode
DECLARE <identifier> : ARRAY[<lbound>:<ubound>] OF <datatype>
DECLARE <identifier> : ARRAY[<lbound1>:<ubound1>,<lbound2>:<ubound2>]
OF <datatype>
Example Single dimensional Array
DECLARE Numbers:ARRAY[1:5] OF INTEGER
1 D array is a list
Example double dimensional Array
DECLARE Sales: ARRAY[1:3,1:5] of real
2D array is a table/ grid
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Example 1 D array
DECLARE Num: ARRAY[1:5] OF Integer
DECLARE Item : INTEGER
DECLARE Index : INTEGER
DECLARE Found : BOOLEAN
DECLARE count : INTEGER
//initialize an array
FOR count  1 To 5
Num[count]  0
ENDFOR
//input in an array
FOR count  1 To 5
OUTPUT ("enter number " & count)
INPUT Num[count]
ENDFOR
//output from an array
FOR count  1 To 5
OUTPUT Num[count]
ENDFOR
'Search in an Array ..... Input what to search
Index  1
Found  False
OUTPUT "Enter Item to search"
INPUT Item
WHILE Index <= 5 AND Found=False
IF Num [Index] = Item
THEN
OUTPUT "item has been found at Index " , Index
Found  True
ENDIF
Index  Index + 1
ENDWHILE
IF Found = False
THEN
OUTPUT "Item is not in the list"
ENDIF
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Q1 a) Make array a global variable and use subroutines
DECLARE Num: ARRAY[1:5] OF Integer
DECLARE count : INTEGER
//initialize an array
PROCEDURE INITIALIZE()
FOR count  1 To 5
Num[count]  0
ENDFOR
ENDPROCEDURE
//input in an array
PROCEDURE ENTER()
FOR count  1 To 5
OUTPUT ("enter number " & count)
INPUT Num[count]
ENDFOR
ENDPROCEDURE
//output from an array
PROCEDURE DISPLAY( )
FOR count  1 To 5
OUTPUT Num[count]
ENDFOR
ENDPROCEDURE
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'Search in an Array ..... Input what to search
PROCDEURE SEARCH( )
DECLARE Item : INTEGER
DECLARE Index : INTEGER
DECLARE Found : BOOLEAN
//LOCAL Variables
Index  1
Found  False
OUTPUT "Enter Item to search"
INPUT Item
WHILE Index <= 5 AND Found=False
IF Num [Index] = Item
THEN
OUTPUT "item has been found at Index " , Index
Found  True
ENDIF
Index  Index + 1
ENDWHILE
IF Found = False
THEN
OUTPUT "Item is not in the list"
ENDIF
ENDPROCEDURE
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Q1 b. Extend your algorithm to write a function SEARCH1( ) that takes parameter Item.
It returns the index at which the item was found in the array. Return -1 If the Item was not
found. Assume the array is a global variable.
FUNCTION Search1 (Item : INTEGER) RETURNS INTEGER
DECLARE Index :INTEGER
DECLARE Found :BOOLEAN
DECLARE IndexFound: INTEGER
Index  1
Found  False
WHILE Index <= 5 AND Found=False
IF Num [Index] = Item
THEN
OUTPUT "item has been found at Index " , Index
Found  True
IndexFound  Index
ENDIF
Index  Index + 1
ENDWHILE
IF Found = False
THEN
OUTPUT "Item is not in the list"
IndexFound  -1
ENDIF
RETURN IndexFound
ENDFUNCTION
(b) Write the corresponding function call to output the value returned. Assume 25 is the
argument.
OUTPUT Search1 (25)
(c) Write the corresponding function call. Assign the value returned to a new variable result.
Assume 25 is the argument.
DECLARE result: INTEGER
result  Search1(25)
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Homework
Modify the above PSEUDOCODE. Implement it as a menu driven program using VB.
Procedure Main ( ) // It will only have a single call
CALL Menu()
END PROCEDURE
PROCEDURE Menu( )
// OUTPUT the following menu
Enter I for Initialisation( )
Enter E for Enter( )
Enter D for Display( )
Enter R for Search using REPEAT loop
Enter F for Search using FOR loop
Enter W for Search using WHILE
//Use CASE structure to call the respective subroutine
//Use a rouge value loop to repeat the menu
ENDPROCEDURE
Home work Q5. 9608/21/M/J/15 Trace Table
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Single Vs Multiple Search results
Single Search Result
(Loop stops at the first occurrence of the match)
Item has been found at Index 3
Multiple Search Result
(Loop continues from lower bound to upper
1
14
2
25
3
70
4
44
5
70
Bound. It displays all the results where a match occurs.)
Item has been found at Index 3
Item has been found at Index 5
To implement multiple search, modify the search subroutine using one of the following


Use simple FOR loop
While Index <= 5 And Found =FALSE

Until Index > 5 Or Found=TRUE
Case sensitive Vs Case insensitive Search
For a string data type array
Evaluate the following conditions
If “CAT”= “cat”
FALSE
If “CAT” = “CAT”
TRUE
Case insensitive search
IF TO_UPPER(words(Index)) = TO_UPPER(item)
If TO_LOWER(words(Index)) = TO_LOWER(item)
Case sensitive search
If ArrayName(Index) = item
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Practice Questions
Solve the following questions using Pseudocode.
(Refer to the search algorithm provided)
Q1. If the data item to be searched exists more than once in the array, which index number will
be displayed?
Q2. Rewrite the single search solution using REPEAT loop
Q3 a. Rewrite the solution given above for multiple search results using WHILE.
Q3 b. Rewrite the solution for multiple search results using REPEAT Loop
Q4. Rewrite the search program for multiple search results using FOR loop
Q5. Why is FOR loop not appropriate for single search result.
Q6. Rewrite the single search solution for searching item 20 in the array.
Q7. Given solution is for case sensitive search. Rewrite it for case insensitive search.
Assume Array StudentNames stores names of 6 students.
(Case insensitive search would consider “ALI”, “aLi” and “ali” as a match for “Ali”).
HINTS
Q1. Only the index corresponding to the first occurrence would be displayed.
Q2. Note the changes (Invert the condition)
WHILE Index <= 5 AND Found =FALSE
UNTIL Index > 5 OR Found=TRUE
Q3 a. Change the while condition to
While Index <= 5 And Not Found
Q3 b.
UNTIL Index > 5
Q4. Make the following changes
Index  1
FOR Index 1 to 5
Index  Index + 1
ENDFOR
Q5. Inefficient. It continues the loop even after the item has been found.
Q6. This is an example of hard code. You do not need to take input from user now.
Q7. Make the following changes
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Pseudocode format - Search Procedure using While loop
Single search result
PROCEDURE Search1( )
DECLARE Index : INTEGER
DECLARE Found : BOOLEAN
DECLARE Item : INTEGER
Index  1
Found  False
OUTPUT "Enter Item to search"
INPUT Item
WHILE Index <= 5 AND Found=False
IF Num [Index] = Item
THEN
OUTPUT "item has been found at Index " , Index
Found  True
ENDIF
Index  Index + 1
ENDWHILE
IF Found = False
THEN
OUTPUT "Item is not in the list"
ENDIF
ENDPROCEDURE
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Pseudocode format - Search Procedure using Repeat loop
Single search result
PROCEDURE Search2( )
DECLARE Index : INTEGER
DECLARE Found : BOOLEAN
DECLARE Item : INTEGER
Index  1
Found  False
OUTPUT "Enter Item to search"
INPUT Item
REPEAT
IF Num [Index] = Item
THEN
OUTPUT "item has been found at Index " , Index
Found  True
ENDIF
Index  Index + 1
UNTIL Index > 5 OR Found=TRUE
IF Found = False
THEN
OUTPUT "Item is not in the list"
ENDIF
ENDPROCEDURE
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Pseudocode format - Search Procedure using FOR loop
(Multiple search results)
PROCEDURE Search3( )
DECLARE Index : INTEGER
DECLARE Found : BOOLEAN
DECLARE Item : INTEGER
Found  False
OUTPUT "Enter Item to search"
INPUT Item
FOR Index  1 to 5
IF Num [Index] = Item
THEN
OUTPUT "item has been found at Index " , Index
Found  True
ENDIF
ENDFOR
IF Found = False
THEN
OUTPUT "Item is not in the list"
ENDIF
ENDPROCEDURE
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Pseudocode Syntax
Example MyProgram is calling InitialiseArray
Subroutine Header
PROCEDURE InitialiseArray(Details:ARRAY OF String)
DECLARE Index : Integer
For Index ← 1 To 5
Details[Index]← ""
ENDFOR
Parameters
End PROCEDURE
PROCEDURE MyProgram()
DECLARE Details[5] : String
//Call to a procedure/Subroutine
Call InitialiseArray(Details)
End PROCEDURE
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Arguments
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Practice questions
Q1.a) Write a subroutine MyMinimum( )



That takes MyArray as a parameter
Outputs the 2nd element from the array
Returns the minimum value from the array
Main( )




Declare array Weight of size 6 (Real data type)
Input data in the array
Call MyMinimum and send Weight as an argument.
Output the minimum value
b) Edit Minimum ( ) and Main ( ) to make the following changes
Main( )




Prompt and input the size of the array Weight
Declare the array Weight
Call MyMinimum. Send Weight and size as arguments.
Output the minimum value
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Bubble sort
Text book page 215
Sorting


Ascending order A-Z (default)
Descending order Z-A
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Concept of PASSES
1
2
3
4
5
6
7
FOR Passes 1 TO Maxlndex – 1
ENDFOR
For 7 elements we need 6 passes
Note : Index 1 to 7
Total Number of elements 7
Required passes = Total elements -1 = 6
Because last element left is always sorted (there is no other element to compare it with).
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PASSES
Within each Pass, compare and swap
FOR Passes 1 TO Maxlndex – 1
FOR Index  1 TO n
//Compare and swap
ENDFOR
ENDFOR
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Within each Pass, compare and swap
FOR Passes 1 TO Maxlndex – 1
FOR Index  1 TO n
IF MyList[Index] > MyList[Index + 1]
THEN
Temp  MyList[Index]
MyList[Index]  MyList[Index + l]
MyList[Index+ 1]  Temp
ENDIF
ENDFOR
ENDFOR
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Compare only n-1 elements in the next pass
1
2
3
4
5
6
7
n  Maxlndex – 1
FOR Passes 1 TO Maxlndex – 1
……
……
n  n - 1 //code will only process n-1 elements in the next loop
ENDFOR
We initialize n with MaxIndex-1 = 6
Because for 7 elements, we have to compare 6 pairs in the first pass
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In the loop :
Compare 5 pairs in pass 2
Compare 4 pairs in pass 3, so on.
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n  Maxlndex – 1
FOR Passes 1 TO Maxlndex – 1
FOR Index  1 TO n
IF MyList[Index] > MyList[Index + 1]
THEN
Temp  MyList[Index]
MyList[Index]  MyList[Index + l]
MyList[Index+ 1]  Temp
ENDIF
ENDFOR
nn-1
ENDFOR
Inefficient algorithm because it will keep iterating even if the array is already
sorted.
Count controlled outer loop for passes should be replaced by a conditional loop.
Main idea is that if we have gone through the whole of the inner loop (one pass) without
swapping any values, we know that the array elements must be in the correct order.
Use a flag (Boolean variable) example NoMoreSwaps
NoMoreSwaps  TRUE
Indicates that there was not a single swap, thus the array has been sorted.
NoMoreSwaps  FALSE
Indicates that there was at least one swap, thus the array is still not sorted.
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n MaxIndex - 1
REPEAT
NoMoreSwaps  TRUE
FOR j  1 TO n
IF MyList [Index] > MyList [Index + l]
THEN
Temp  MyList[Index]
MyList[Index]  MyList[Index + 1]
MyList[Index + 1]  Temp
NoMoreSwaps  FALSE
ENDIF
ENDFOR
nn-1
UNTIL NoMoreSwaps = TRUE
Practice
Q3. 9608/22/O/N/17 bubble sort
Q3. 9608/21/O/N/17 bubble sort
Q5. 9608/22/O/N/15 trace table
1D array
Q3a,b 9608/21/M/J/19
Homework
9608/22/O/N/16 Q6 & Q4
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2D Array
[1] Name
[2] Email
[3] DOB
[4] ID
[1]
Ali
abc@gmail.com
25/05/2010
D3452-B
[2]
Saman
xyz@gmail.com
15/07/2012
C3752-B
[4]
John
65sdf7@gmail.com
15/05/2011
C3482-B
[5]
Sahil
weds@gmail.com
01/01/2016
C3432-V
[3]
2D Array
Details[1:5,1:4] indicates rows 1 to 5 and columns 1 to 4
1 row represents 1 record
Element 01/01/2019
At Index [5,3]
2D array is a grid or a Table
Data type
That is (Row,Column)
All elements in an array are of the same data type
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2D ARRAY
PROCEDURE TwoDArray()
DECLARE Num:ARRAY [1:2, 1:4] OF INTEGER
DECLARE Row : INTEGER
DECLARE Col : INTEGER
DECLARE Item : INTEGER
DECLARE Found : BOOLEAN
//initialize an array
FOR Row  1 To 2
FOR Col  1 To 4
Num[Row, Col]  0
ENDFOR
ENDFOR
//input in an array
For Row  1 To 2
For Col  1 To 4
OUTPUT("enter number")
INPUT Num[Row, Col]
ENDFOR
ENDFOR
//formatted output
FOR Row  1 To 2
FOR Col  1 To 4
OUTPUT(Num[Row, Col] & "
ENDFOR Col
")
//OUTPUT NEWLINE
ENDFOR Row
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//search in double dimensional array
Found  False
OUTPUT("Enter item to search")
INPUT Item
FOR Row  1 To 3
FOR Col  1 To 4
IF Num[Row, Col] = Item
THEN
OUTPUT("Item has been found at " & Row & " , " & Col)
Found  TRUE
EXIT PROCEDURE
ENDIF
ENDFOR Col
ENDFOR Row
IF Found = FALSE
THEN
OUTPUT("Item does not exist in the array")
ENDIF
ENDPROCEDURE
//Alternative correct solutions exist for search
Pseudocode- 2D array passed as a parameter
//PROCEDURE header
PROCEDURE TEST(DETAILS:ARRAY OF String)
Parameter
passing of 1D
and 2D array
is identical in
pseudocode.
//Call to a PROCEDURE
Call TEST(Details)
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//Global variable declarations
DECLARE ProductionData:ARRAY [1:4, 1:3] OF INTEGER
DECLARE Row : INTEGER
DECLARE Col : INTEGER
//output the production data of day3
PROCEDURE OUTPUT()
FOR Col  1 To 3
OUTPUT ProductionData [3, Col]
ENDFOR
ENDPROCDEURE
//Input the production data of Worker1 for all 4 days
PROCEDURE INPUT()
FOR Row  1 To 4
OUTPUT “Enter data”
INPUT ProductionData [Row, 1]
ENDFOR
ENDPROCDEURE
//OUTPUT the production data of Worker2 day3
PROCEDURE CELL()
OUTPUT ProductionData [3, 2]
ENDPROCDEURE
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Practice question: Q5 9608/23/M/J/15 Trace table (1D & 2D)
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File Operations
Files are permanent storage of data. Data is stored in the memory even after the program closes.
Arrays are temporary storage of data. Data is lost as soon as the program closes.
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File handling
File Operations –Pseudocode
WRITE
Program
File
READ
DECLARE data : STRING
data ← "Hello"
//open file to write data on the file
OPENFILE("TESTFILE.txt" FOR WRITE)
WRITEFILE(“TESTFILE.txt” , data)
CLOSEFILE(“TESTFILE.txt”)
// Open file to append. Insert at the end of file.
OPENFILE("TESTFILE.txt" FOR APPEND)
WRITEFILE(“TESTFILE.txt” , data)
CLOSEFILE(“TESTFILE.txt”)
// Open file to read data from file.
OPENFILE("TESTFILE.txt" FOR READ)
WHILE NOT EOF(“TESTFILE.TXT”)
READFILE (“TESTFILE.txt”, data)
ENDWHILE
CLOSEFILE(“TESTFILE.txt”)
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Example1- Write data on file
Q. Write 4 items of data, entered by the user, onto the file.
DECLARE data : STRING
DECLARE count : INTEGER
OPENFILE("TESTFILE.txt" FOR WRITE)
FOR count  1 To 4
OUTPUT ("Enter data") 'prompt
INPUT Data
WRITEFILE(“TESTFILE.txt” , data)
ENDFOR
CLOSEFILE(“TESTFILE.txt”)
NOTE: In Output mode if a file already exists, it will be overwritten. If it does not exist, a new file
will be created automatically.
Open and close files are always outside the loop
If file is open in one mode it cannot be opened in another mode until it is closed.
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Teacher : Huma Imad
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Example 2a- Append data
DECLARE Data : STRING
Data  "hello"
OPENFILE("TESTFILE.txt" FOR APPEND)
WRITEFILE(“TESTFILE.txt” , data)
CLOSEFILE(“TESTFILE.txt”)
Example 2b-Append Data in a loop
DECLARE Data : STRING
OPENFILE("TESTFILE.txt" FOR APPEND)
FOR count  1 To 3
OUTPUT("Enter data")
INPUT Data
//Append line at the end of file
WRITEFILE(“TESTFILE.txt” , data)
ENDFOR
CLOSEFILE(“TESTFILE.txt”)
Append means to add data to the end of file (Does not overwrite file)
If the file does not exist, a new file is created.
If the question does not say create a new file then go for the append mode.
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Example 3 – Read data from file
DECLARE data: STRING
OPENFILE("TESTFILE.txt" FOR READ)
WHILE NOT EOF(“TESTFILE.TXT”)
READFILE (“TESTFILE.txt”, data)
OUTPUT data
ENDWHILE
CLOSEFILE(“TESTFILE.txt”)
Note
If the file doesn’t exist, OPENFILE will give a run time error.
If file is already open in another mode, it should be closed first and
then opened FOR READ.
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Using 2 files
Read data from FileA
Convert the data into uppercase
Save the data in FileB
DECLARE data : STRING
OPENFILE("FileA.txt" FOR READ)
OPENFILE("FileB.txt" FOR WRITE)
WHILE NOT EOF(“FileA.TXT”)
READFILE (“FileA.txt”, data)
data  UCASE (data)
WRITEFILE(“FileB.txt” , data)
ENDWHILE
CLOSEFILE(“FileA.txt”)
CLOSEFILE(“FileB.txt”)
NOTE
We cannot edit or delete anything in a text file. In order to make changes or delete data, create
another file. Leave the original file unchanged.
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Rouge Value & File handling
DECLARE ID :STRING
DECLARE options : CHAR
OPENFILE("TESTFILE.txt" FOR WRITE)
REPEAT
OUTPUT("Enter ID")
INPUT ID
WRITEFILE(“TESTFILE.txt” , ID)
OUTPUT("Do you want to enter another ID? Enter N for no,
other key for Yes")
INPUT options
press any
UNTIL options = ‘N’
CLOSEFILE(“TESTFILE.txt”)
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Menu driven file operations program. Assume FileName is a global variable.
DECLARE FileName : STRING
//Global variable
PROCEDURE MENU( )
DECLARE choice : CHAR
DECLARE Data : STRING
DECLARE count : INTEGER
//Any subroutine can assign the value to the global variable
FileName  “Employee.txt”
REPEAT
OUTPUT("Enter R for Read data from file, Enter A for Append,")
OUTPUT("Enter W for Writing data, Enter E to end program ")
INPUT choice
CASE OF choice
‘W’: CALL WriteNow( )
‘A’: CALL AppendNow( )
‘R’: CALL ReadNow( )
‘E’: End
// end program
OTHERWISE OUTPUT("invalid entry")
ENDCASE
UNTIL False
//infinite loop
ENDPROCEDURE
//CONTINUED ON THE NEXT PAGE
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PROCEDURE ReadNow( )
DECLARE data: STRING
OPENFILE(FileName FOR READ)
WHILE NOT EOF(FileName)
READFILE (FileName, data)
OUTPUT data
ENDWHILE
CLOSEFILE FileName
ENDPROCEDURE
PROCEDURE AppendNow( )
DECLARE Data : STRING
OPENFILE(FileName FOR APPEND)
OUTPUT("Enter data")
INPUT Data
WRITEFILE(FileName, data)
CLOSEFILE FileName
ENDPROCEDURE
PROCEDURE WriteNow( )
DECLARE data : STRING
OPENFILE(FileName
FOR WRITE)
OUTPUT ("Enter data")
INPUT Data
WRITEFILE(FileName
, data)
CLOSEFILE FileName
ENDPROCEDURE
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PROCEDURE WriteOperation(FileName as STRING)
//Corresponding CALL is as follows
CALL WriteOperation ("Students.txt")
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9608/21/O/N/17
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2 different file structures
9608/21/O/N/16
ID 0198 indicates
string datatype
because of
leading zero
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Teacher : Huma Imad
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Q1.Use the file structure shown. (a) Write a procedure ReadNow( ) that takes FileName as a
parameter. It reads and outputs all the records from the text file. (b) Write a procedure AppendNow( )
that takes FileName as a parameter and inserts new record in the text file.
0198
Onion
23.56
(a)PROCEDURE ReadNow(FileName :STRING )
DECLARE ID: STRING
DECLARE Description: STRING
DECLARE StrPrice :STRING
DECLARE Price:REAL
OPENFILE(FileName FOR READ)
2456
WHILE NOT EOF(FileName)
READFILE (FileName, ID)
OUTPUT (“ID IS ” & ID)
Mango
34.99
READFILE (FileName, Description)
OUTPUT (“Desc is” & Description)
….. ….
…. ……
READFILE (FileName, StrPrice)
Price STRING_TO_NUM (StrPrice)
OUTPUT (“Price is ” & Price)
ENDWHILE
CLOSEFILE FileName
ENDPROCEDURE
(b)PROCEDURE AppendNow(FileName :STRING )
DECLARE ID: STRING
DECLARE Description: STRING
DECLARE Price: REAL
OPENFILE(FileName FOR APPEND)
OUTPUT("Enter ID")
INPUT ID
WRITEFILE(FileName, ID)
OUTPUT("Enter Description")
INPUT Description
WRITEFILE(FileName, Description)
OUTPUT("Enter Price")
INPUT Price
WRITEFILE(FileName, Price)
CLOSEFILE FileName
ENDPROCEDURE
NOTE: EACH DATA ITEM BECOMES STRING WHEN STORED IN A TEXT FILE.
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Q2.Use the file structure shown. (a) Write a procedure ReadNow( ) that takes FileName as a
parameter. It reads and outputs all the records from the text file. (b) Write a procedure AppendNow( )
that takes FileName as a parameter and inserts new record in the text file.
0198Onion34.50
Assume
0786Mango12.99
ID is 4 characters long
0124Apple12.50
Description is variable length
….
Price is 5 characters long
….
(a)PROCEDURE ReadNow(FileName :STRING )
DECLARE data:STRING
DECLARE ID: STRING
DECLARE Description: STRING
DECLARE Price: REAL
DECLARE StrPrice :STRING
DECLARE Pos :INTEGER
OPENFILE(FileName FOR READ)
WHILE NOT EOF(FileName)
READFILE (FileName, data)
ID  LEFT(data, 4)
Description  MID(data, 5, LENGTH(data)-9)
StrPriceRIGHT(data, 5)
Price STRING_TO_NUM (StrPrice)
OUTPUT (“ID IS ” & ID)
OUTPUT (“Desc is” & Description)
OUTPUT (“Price is ” & Price)
ENDWHILE
CLOSEFILE FileName
ENDPROCEDURE
0198
Onion
34.50
4
+x
+5
LENGTH(data)=4+x+5
Apply
formula
x = LENGTH(data)-(4+5)
x = LENGTH(data) -9
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(b)PROCEDURE AppendNow(FileName :STRING )
DECLARE ID: STRING
DECLARE Description: STRING
DECLARE Price: REAL
OPENFILE(FileName FOR APPEND)
OUTPUT("Enter ID")
INPUT ID
WRITEFILE(FileName, ID)
OUTPUT("Enter Description")
INPUT Description
WRITEFILE(FileName, Description)
OUTPUT("Enter Price")
INPUT Price
WRITEFILE(FileName, Price)
CLOSEFILE FileName
ENDPROCEDURE
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Q1.Write a procedure TEST( ) that takes a string array MyArray as a parameter. It copies the first 5
elements of MyArray to a new file MyFile.txt.
Answer
PROCEDURE TEST(MyArray:Array OF STRING)
DECLARE Data : STRING
DECLARE count : INTEGER
OPENFILE(“MyFile.txt” FOR WRITE)
FOR count 1 to 5
WRITEFILE(“MyFile.txt”, MyArray[count])
ENDFOR
CLOSEFILE “MyFile.txt”
ENDPROCEDURE
Q2.Write a procedure FINAL( ) that takes a STRING array MyArray as a parameter. It copies the first 5
lines from MyFile.txt to Array MyArray.
Answer
PROCEDURE FINAL( MyArray: ARRAY OF STRING)
DECLARE count :INTEGER
OPENFILE(“MyFile.txt” FOR READ)
FOR count 1 to 5
READFILE (“MyFile.txt”, MyArray[count])
ENDFOR
CLOSEFILE “MyFile.txt”
ENDPROCEDURE
Practice question
Q5 (b) May/June 2016 9608 P21
9608/22/O/N/17 Homework
Teacher : Huma Imad
141 | P a g e
P2 Computer Science 9618
Searching in a Text File Vs Searching in an Array
PROCEDURE search(FileName : STRING, item : STRING)
DECLARE Found : Boolean
DECLARE data : String
OPENFILE(FileName
Found  False
FOR READ)
WHILE NOT EOF(FileName) And Found = False
READFILE (FileName, data)
If data = item
THEN
OUTPUT ("item has been found")
Found  True
ENDIF
ENDWHILE
IF Found = False
THEN
OUTPUT("Item is not in the file")
ENDIF
CLOSEFILE FileName
ENDPROCEDURE-------------------------------------------------------------PROCEDURE searchInArray(MyArray:ARRAY OF STRING, item : String)
DECLARE Found : Boolean
DECLARE data : String
DECLARE Index : Integer
Found  False
Index  1
//Assume Array has upperbound 5
WHILE Index <= 5 And Found = False
data  MyArray(Index)
IF data = item
THEN
OUTPUT("item has been found at Index " & Index)
Found  True
ENDIF
Index = Index + 1
END WHILE
IF Found = False
THEN
OUTPUT("Item is not in the Array")
ENDIF
ENDPROCEDURE
Teacher : Huma Imad
142 | P a g e
P2 Computer Science 9618
SUMMARY OF FORMATS
Input
INPUT Marks
Output
OUTPUT Marks
Comment
//This is a comment
Built-in
MOD(10,3)
functions
DIV( 10,3)
Result ← 2^3
Num ← INT (3.5)
Num ← 5/2
Otherwise as per the CAIE INSERT
Teacher : Huma Imad
143 | P a g e
P2 Computer Science 9618
Iteration
FOR X←1 TO 10
…
ENDFOR
WHILE COUNT<10
ENDWHILE
REPEAT
UNTIL count=10
Selection
IF count>1
THEN
OUTPUT “TRUE”
ELSE
OUTPUT “FALSE”
ENDIF
Teacher : Huma Imad
144 | P a g e
P2 Computer Science 9618
SELECTION
Pseudocode
CASE OF ______
CASE OF _________
CASE OF ____
‘A’: ____
“Apple”: _____
1: ________
‘B’:____
“Banana”:____
2:________
‘C’: ____
“Mango”: _____
3: ________
OTHERWISE _____
OTHERWISE _____
OTHERWISE
ENDCASE
ENDCASE
ENDCASE
OTHERWISE IS OPTIONAL
String
CHR(S)
Operations
ASC( S)
LENGTH(S)
LEFT(S, L)
RIGHT (S, L)
MID(S, P, L)
TO_UPPER( )
Teacher : Huma Imad
145 | P a g e
P2 Computer Science 9618
TO_LOWER( )
UCASE( )
LCASE( )
Concatenation “Wi” & “Fi”
//PREFERRABLE
“Wi” + “Fi”
Random
Num←
Number
RANDOMBETWEEN(MIN,MAX)
//INTEGER NUMBER
Num← RND( ) //REAL NUMBER BETWEEN 0-1
PROCEDURE ADD(Num1 : INTEGER)
……
ENDPROCEDURE
Procedure Call Call Add(2)
Call Add(x)
Teacher : Huma Imad
146 | P a g e
P2 Computer Science 9618
FUNCTION ADD(NUM1 : INTEGER) RETURNS INTEGER
……
RETURN RESULT
ENDFUNCTION
//Note
RETURNS in the header
RETURN at the end
Function Call
Answer←Add(4)
Answer←Add(num1)
OUTPUT(Add(4))
Num←Add(x) + 2
Teacher : Huma Imad
147 | P a g e
P2 Computer Science 9618
Parameter Passing
PROCEDURE Test(BYVALUE x)
PROCEDURE Test(BYREF y)
Declaration
DECLARE Prices: ARRAY [1: 5] OF CURRENCY
1D Array
DECLARE Num: ARRAY [0: 9] OF INTEGER
//Note
//It has LowerBound and UpperBound both
1D Array as a parameter
PROCEDURE TEST(DETAIL:ARRAY OF String)
1D Array as an argument
Call TEST(Detail)
2D Array
DECLARE Data: ARRAY [1: 4, 1:3] OF INTEGER
Declaration
//4 Rows and 3 columns
DECLARE Sale: ARRAY [0: 4, 0:3] OF INTEGER
//5 Rows and 4 columns
2D Array as a parameter
PROCEDURE TEST(DETAILS:ARRAY OF STRING)
//Same as 1D
2D argument
Call TEST(Details)
//Same as 1D
Teacher : Huma Imad
148 | P a g e
P2 Computer Science 9618
File Operations
OPENFILE("TESTFILE.txt" FOR WRITE)
OPENFILE("TESTFILE.txt" FOR APPEND)
OPENFILE("TESTFILE.txt" FOR READ)
WRITEFILE(“TESTFILE.txt” , data)
READFILE (“TESTFILE.txt”, data)
EOF(“TESTFILE.TXT”)
CLOSEFILE(“TESTFILE.txt”)
Teacher : Huma Imad
149 | P a g e