This document discusses repetition and loops in the C programming language, emphasizing the necessity of executing code blocks multiple times. It outlines three types of loops—while, for, and do-while—and explains their structures and use cases, including the significance of conditions for executing loop bodies. The material is intended for students in a structured programming course to aid their understanding of flow control in programming.

1. CSE-1203
Structured Programming Language
Lecture 6
Repetition/Loops Part-I
Md. Rafsan Jani
Assistant Professor
Department of Computer Science and Engineering
Jahangirnagar University

2. Outline
Iterations in C
– while statement
– for statement
– do…while statement
– Infinity Loop
– Comparison
January 12, 2025 Md. Rafsan Jani, Assistant Professor, Dept. of CSE, JU 2

3. Loop
 You may encounter situations, when a block of code needs to
be executed several number of times. In general, statements
are executed sequentially: The first statement in a function is
executed first, followed by the second, and so on.
 Programming languages provide various control structures
that allow for more complicated execution paths.
 A loop statement allows us to execute a statement or group
of statements multiple times.
January 12, 2025 Md. Rafsan Jani, Assistant Professor, Dept. of CSE, JU 3

4. Example 1
 What if we want to process
three different pairs of integers?
January 12, 2025 Md. Rafsan Jani, Assistant Professor, Dept. of CSE, JU 4

5. Example 2
 One solution is to copy and paste the necessary lines
of code. Consider the following modification:
 What if you wanted to process four sets?
Five? Six? ….
January 12, 2025 Md. Rafsan Jani, Assistant Professor, Dept. of CSE, JU 5

6. Processing an arbitrary number of
pairs
 We might be willing to copy and paste to process a
small number of pairs of integers but
 How about 1,000,000 pairs of integers?
 The solution lies in mechanisms used to control the
flow of execution
 In particular, the solution lies in the constructs that
allow us to instruct the computer to perform a task
repetitively
January 12, 2025 Md. Rafsan Jani, Assistant Professor, Dept. of CSE, JU 6

7. Repetition (Looping)

 Use looping when you want to execute a block of code
several times
 Block of code = Body of loop
 C provides three types of loops
while statement
 Most flexible
 No ‘restrictions’
for statement
 Natural ‘counting’ loop
do-while statement
 Always executes body at least once
1
2
3
January 12, 2025 Md. Rafsan Jani, Assistant Professor, Dept. of CSE, JU 7

8. The while Repetition Structure
 Repetition structure
 Programmer specifies
 Condition under which actions will be executed
 Actions to be repeated
 Psuedocode
While there are more items on my shopping list
Purchase next item and cross it off my list
 while loop repeated
 As long as condition is true
 Until condition becomes false
January 12, 2025 Md. Rafsan Jani, Assistant Professor, Dept. of CSE, JU 8

9. The while Repetition Structure
• The condition is
tested
• If the condition is
true, the loop body
is executed and the
condition is
retested.
• When the condition
is false, the loop is
exited.
condition
loop body
false
true
next stmt
January 12, 2025 Md. Rafsan Jani, Assistant Professor, Dept. of CSE, JU 9

10. The while Repetition Structure
 Syntax:
while (expression)
basic block
 Expression = Condition
to be tested
 Resolves to true or false
 Basic Block = Loop Body
 Reminder – Basic Block:
 Single statement or
 Multiple statements
1
January 12, 2025 Md. Rafsan Jani, Assistant Professor, Dept. of CSE, JU 10