EKT 150 – Computer Programming
Laboratory Exercise
LAB 5
SELECTION STRUCTURES
School of Computer and Communication Engineering
Universiti Malaysia Perlis
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EKT 150 – Computer Programming
Laboratory Exercise
1. OBJECTIVES:
1.1 Introduction to if, if …. else, nested if and switch statements.
1.2 Able to use selection control structures in programs.
1.3 Able to modify program according to user requirements.
2 INTRODUCTION:
In C language, there are several selection methods which can be used:
(a) One way selection
(b) Two way selection
(c) Multi selection
(d) Nested if …
(e) Switch command
2.1 One way selection statement
The syntax for one way selection is as below:
if (condition)
statement;
Compound statement: a group of statements bracketed by { and } that are
executed sequentially. ‘{‘ (open curly bracket) and ‘}’ (close curly bracket) must
be used to show the start and end of the commands under the ‘if’ statement.
if (condition)
{
Flowchart:
statement1;
statement2;
start
}
condition
Yes
statement1
No
2.2 Two way selection statement
The syntax for two way selection is as below:
if (condition)
statement;
or
if (condition)
{
else
statement1;
statement;
statement2;
}
else
{
statement1;
statement2;
}
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EKT 120 – Computer Programming
Laboratory Module
Flowchart:
start
statement2
No
condition
Yes
statement1
2.3 Multi selection statement
The syntax for multi selection statement is as below:
Flowchart:
if (condition)
statement;
else if (condition)
statement;
else
statement;
start
condition
T
statement1
F
condition
T
statement1
F
statement1
end
2.4 Nested if statement
Nested if statement is when one if statement is placed inside another if statement.
The nested if statement is used to code decisions with multiple alternatives. The
nested if selection can be modified with the use of logic operator (AND) to combine
two or more conditional (relation) statements to be as one condition statement, thus
omits the nested if statement.
Nested if
Use of logic operator
if (condition)
if (condition)
statement;
else if (condition)
statement;
else
statement;
if ((condition) && (condition))
statement;
else
statement;
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EKT 150 – Computer Programming
Laboratory Exercise
Flowchart:
start
condition
T
F
condition
statement1
statement1
statement2
statement1
end
2.5 Switch statement
The switch statement is another way to do multi selections statement. The syntax is
as follow:
switch (variable)
{
case value1: printf(“Message 1”);
break;
case value2: printf(“Message 2”);
break;
case value3: printf(“Message 3”);
break;
case value4: printf(“Message 4”);
break;
case value5: printf(“Message 5”);
break;
default: printf(“Default Message”);
}
Note: The break statement is used to end the switch after the category or selection is selected.
Omitting the break statement will not generate a syntax error in your program but it will produce
semantic error.
Question: Find out what are syntax and semantic errors.
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EKT 150 – Computer Programming
Laboratory Exercise
3 TASKS:
3.1
(a) The following code segment is syntactically correct, but difficult to read. Rewrite
the segment using indentation that improves its readability.
if (cRoadStat == 's')
if (fTemp > 0)
printf("Roads wet.\n");
else
printf("Roads icy.\n");
else
printf("Roads dry.\n");
(b) Rewrite the following if statement as an equivalent switch statement. The
variable digit is of type int.
if (iDigit == 0)
iValue = 3;
else if (iDigit == 1)
iValue = 3;
else if (iDigit == 2)
iValue = 6;
else if (iDigit == 3)
iValue = 9;
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EKT 150 – Computer Programming
Laboratory Exercise
(c) The decision table below shows fines imposed for speeding violations. Write a
code segment that assigns the correct fine to type double variable fine based on
the value of type int variable speed.
Speed (mph)
65 or less
66-70
71-75
76-80
over 80
Fine ($)
0
15.00
30.00
75.00
100.00
(d) Evaluate the expression below assuming a is 5, flag is 1, and c is 15. What part
of the expression is not computed at all because of short-circuit evaluation?
a != 3 && flag || c >= 10
(e) Write the output for the following code segment.
v1 = 15.0;
v2 = 0.5;
if (v1 > 10.0)
printf("ten ");
else if (v1 > 14.0)
printf("fourteen ");
if (v2 * v1 > 7.0)
printf("seven ");
if (v1 - v2 > 9.0)
printf("nine ");
printf("\n");
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EKT 150 – Computer Programming
Laboratory Exercise
3.2 Write an interactive program that contains an if statement that may be used to
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compute the area of square (area = side ) or a triangle (area = ½ x base x height )
after prompting the user to type the first character of the figure names (S or T).
a. Write down the flowchart for the program.
b. Write your program based on flowchart in (a).
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EKT 150 – Computer Programming
Laboratory Exercise
3.3 Write a program for the National Earthquake Information centre implementing the
following decision table to characterize an earthquake based on its Richter scale
number.
Richter Scale Number (N)
Characterization
N < 5.0
Little or no damage
5.0 ≤ N ≤ 5.5
Some damage
5.5 ≤ N ≤ 6.5
Serious damage: wall may crack or fall
6.5 ≤ N ≤ 7.5
Disaster: house and buildings may collapse
higher
Catastrophe: most buildings destroyed
a. Write down the flowchart for the program.
b. Can you handle this problem with a switch statement? If so, use a switch
statement; if not, explain why;
c. Write a program based on flowchart in (a).
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EKT 150 – Computer Programming
Laboratory Exercise
3.4 Write a nested if statement for the decision diagrammed in the accompanying
flowchart. Use a multiple-alternative if for intermediate decisions where possible.
false
pH == 7
“Neutral”
true
false
“Alkaline”
true
“Very Alkaline”
false
“Very Acidic”
true
pH < 12
true
false
pH > 2
pH > 7
“Acidic”
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EKT 150 – Computer Programming
Laboratory Exercise
3.5 Write a program that takes the x-y coordinates of a point in the Cartesian plane and
displays a message telling either an axis on which the point lies or the quadrant in
which it is found.
y
QII
QI
x
QIII
QIV
Sample lines of output:
(-1.0, -2.5) is in quadrant III
(0.0, 4.8) is on the y axis
a. Write down the flowchart for the program.
b. Write a program based on flowchart in (a).
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EKT 150 – Computer Programming
Laboratory Exercise
3.6 Write a program that assigns to the variable lumens the expected brightness of a
standard light bulb whose power has been stored in watts. Use the following table:
Power (Watts)
15
25
40
60
75
100
Brightness (Lumens)
125
215
500
880
1000
1675
Assign -1 to lumens if the value of watts is not in the table.
a. Write down the flowchart for the program.
b. Write a switch statement based on flowchart in (a).
c. Write a nested if statement equivalent to the switch statement (b) based on
flowchart in (a).
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