Problem Solving
Using Computer
Chapter 2
Prepared by
Kabin Devkota
Udita Bista
C Programming
Problem Solving Steps
1. Problem Analysis
2. Algorithm development and flowchart
3. Pseudocode
4. Coding
5. Compilation and Execution
6. Debugging and testing
7. Program Documentation
1. Problem Analysis
client's problem are properly analyzed
gives a clear, concise problem statement
should specify the following tasks:
a. well defined objectives
b. input requirements
c. output requirements
d. processing requirements
e. feasibility analysis
2. Algorithm development and flowchart
Algorithm
A set of ordered steps required to develop a program
written without any programming language specific symbols/syntax
Guidelines
use plain language
do not use any programming language syntax
every job to be done should be described clearly
single entry and exit point
Properties of excellent algorithm
a.
b.
c.
d.
e.
finiteness : finite number of steps
definiteness : action of each step should be defines clearly without ambiguity
input : inputs should be defined precisely
output : algorithm should result in one or more output
effectiveness : should be more effective among different ways of solving
problems
Flowchart
algorithm in a diagrammatic form that illustrates the sequence of operations
to be performed
facilitates communication between programmers and business people
Advantages of using flowcharts
a. Communication
b. Effective analysis
c. Proper documentation
d. Efficient coding
e. Proper debugging
f. Efficient program maintenance
Symbols
used in
flowchart
Basic guidelines to be followed to draw a flowchart
i. Standard flowchart symbols should be used according to the purpose.
ii. There should be a logical start and stop.
iii. It should be clear, neat and easy to follow. There should not be any room for
ambiguity in understanding the flowchart.
iv. The direction of the flow of a procedure or system is from left to right or top
to bottom
v. English like language should be used in flowcharts, not specific programming
language
vi. It is useful to test the validity of the flowchart be passing through it with a
simple test data
add two numbers
Algorithm
Step 1 : Start
Step 2 : Declare variable a,b,sum
Step 3 : Read values of a and b
Step 4: Add a and b and assign the result to sum
sum
a+b
Step 6: Print sum
Step 7: Stop
Flowchart
3. Pseudocode
natural language construct modelled to look like statements available in many
programming language
mixture of structured english and actual code that is used in program
development
pseudocode is made up of statements written to depict the steps, in the
correct sequence, required to solve a specific problem
begin
read values of a and b
calculate a+b
sum = a+b
print sum
end
Why is pseudocode necessary?
helps to understand the program specifications in advance
programmers will have encountered most of the possible problems and
know the possible solutions
boosts software development techniques by reducing time and increasing
efficiency
easier to read and understand
Write algorithm, pseudocode, flowchart to read marks of a student in a
subject and display whether he is pass or fail in the exam. The pass mark
is 40
Algorithm
Pseudocode
Step 1: Start
Step 2: Declare variable marks
Step 3: Read marks
Step 4: check marks
if marks greater than or equal
to 40 then
display pass
else
display fail
Step 5: Stop
begin
read marks in a subject
IF marks >= 40 THEN
print pass
ELSE
print fail
ENDIF
end
Flowchart
4. Coding
process of transforming algorithm or flowchart into computer understandable
form
can be done in any higher or low level language
Tips for good programming
follow the standards of coding i.e. proper indentations and comments
always use meaningful names and labels
keep modules short
make modules general such that it can be used for other purpose
5. Compilation and execution
the process of converting a program written in high level language(source
code) to an executable program
source code is converted to object code through a compiler
then, object code is linked with the library functions through linker; this gives
real values to all the symbolic address in the object code, thereby producing an
executable program
Source program
Compiler
Object code/file
Runtime library/
library function
Linker
Executable program
6. Debugging and testing
process of detecting and removing errors in a program
Types of errors
a. Syntax error: results when rules of language(i.e. syntax) is violated
b. Run-time error: errors such as mismatch of datatypes, referencing an out
of range array elements
c. Logical error: errors related to logic of the program execution; actions as
taking the wrong path, failure to consider a particular condition and
incorrect evaluation of statements
d. Latent error: hidden errors that show up only when particular set of data is
used(eg. a=(x+y)/(p-q), this generates error when p=q)
Debugging techniques
a. Error isolation: locating errors by deleting certain portion of code and
executing it again to check if the error appears or not
b. Tracing: printing values of important variables at different stages of a
program and deciding whether values are correct or not
c. Watch values: watching value of a variable or expresison continuously as
the program executes
d. Breakpoints: a temporary stopping point within programs; can check for
errors until the breakpoints
e. Stepping: process of executing one instruction at a time
Testing
process of executing a program or running a system with the intent of finding
errors
improves quality
verification and validation
a. Human Testing
code inspection by programmer and test group
review by peer group
b.Computer based testing(compiler testing and run-time testing)
running programs with test data to check whether they give correct or not
Testing procedure
i. Black Box Testing
it is an external test called functional test in which the program is tested to
check whether it performs properly or not
it is the test of input/output behavior without considering the internal
structure of the test objects
ii. White Box Testing
it is a line-by-line testing method in which interior errors are examined and
recovered
it is concerned with the correctness of each statement
7. Program documentation
all the processes must be properly documented for future reference
it is the process of making a program well structured by using appropriate
comments and other techniques
Merits of documentation
it increases the interaction between software and individual who manage it
and improves user efficiency
it is very important to make a software more attractive
Write algorithm and flowchart to find the greatest number
among three numbers
Algorithm First Way
Step 1: Start
Step 2: Declare variables a, b, c
Step 3: Read a, b, c
Step 4: Check a, b, c
if a > b and a > c then
display a is greatest
else if b > a and b > c then
display b is greatest
else
display c is greatest
Step 5: Stop
Algorithm Second Way
Step 1: Start
Step 2: Declare variables a, b, c
Step 3: Read a, b, c
Step 4: Check a, b, c
if a > b then
if a > c then display a is greatest
else display c is greatest
else
if b > c then display b is greatest
else display c is greatest
Step 5: Stop
Write algorithm and flowchart to check if a number if exactly
divisible by 5 but not by 7
Algorithm
Step 1: Start
Step 2: Declare variables n
Step 3: Read n
Step 4: Check n
if n mod 5 is equal to 0 and n mod 7 is not equal to 0 then
display yes
else
display no
Step 9: Stop
Write algorithm and flowchart to calculate the factorial of a
given number
Algorithm
Step 1: Start
Step 2: Declare variables n, fact
Step 3: Read n
Step 4: if n = 0, display 1
Step 5: Set value of fact = 1
Step 6: Calculate fact as fact = fact * n
Step 7: n <-- n - 1
Step 8: Repeat steps 6 and 7 until n becomes 0
Step 9: Display fact
Step 10: Stop
Write algorithm and flowchart to display a fibonacci series
upto a given number of terms
Algorithm
Step 1: Start
Step 2: Declare variables a, b, c, n
Step 3: Read n
Step 4: Set the values of a <-- 0 and b <-- 1
Step 5: Display a and b
Step 6: Calculate c using c <-- a + b
Step 7: Display c
Step 8: Set the values of a and b as
a <-- b, b <-- c
Step 9: Repeat steps 6 to 8 (n-3) times
Step 10: Stop
Flowchart
Write algorithm and flowchart to swap values of two variables
Algorithm
Step 1: Start
Step 2: Declare variables a,b,temp
Step 3: Set values of a and b
Step 4: Display a and b
Step 5: Perform the operations
temp <-- a
a <-- b
b <-- temp
Step 6: Display a and b
Step 7: Stop
Flowchart
Write algorithm and flowchart to convert an alphabet which is in capital
to small and vice versa
Algorithm
Step 1: Start
Step 2: Declare variable c
Step 3: Read character c
Step 4: Display c
Step 5: If c is greater than or equal to 97 and c is less than or equal to 122 then
convert c into small using
c <-- c - 32
else if c is greater than or equal to 65 and c is less than or equal to 90 then
c <-- c + 32
else
display invalid input and go to step 7
Step 6: Display c
Step 7: Stop
Flowchart