1. Lec 6 Loop Statements Introduction to Computer Programming
KIC
5/22/2019
Department of Information Technology.
Introduction to Computer Programming
Lec 6
Loop Statements
KIC/Introduction to Computer Programming
5/22/2019
Introduction to Computer Programming

2. KIC/Introduction to Computer Programming
Outlines
Repetition Statements
for repetition statements
while repetition statements
do…while repetition statements
5/22/2019
KIC/Introduction to Computer Programming

3. KIC/Introduction to Computer Programming
All programs can be broken down into 3 controls:
Sequence–handled automatically by compiler
Selection – if, if…else , switch
Repetition – for, while, do…while
5/22/2019
KIC/Introduction to Computer Programming

4. Repetition Statements
Computer executes group of instructions repeatedly while some condition remains true
Counter-controlled repetition:
Definite repetition: know how many times loop will execute
Control variable used to count repetitions
Counter-controlled repetition requires:
The name of a control variable (or loop counter)
The initial value of the control variable
An increment (or decrement) by which the control variable is modified each time through the loop
A condition that tests for the final value of the control variable (i.e., whether looping should continue)
5/22/2019
KIC/Introduction to Computer Programming

5. for Repetition Statements
{body for the loop (statements) }
for (int count = 1; count < = 10; count++) {
printf (“%d ”, count); }
No semicolon (;) after last expression
5/22/2019
KIC/Introduction to Computer Programming

6. KIC/Introduction to Computer Programming
5/22/2019
KIC/Introduction to Computer Programming

7. 7
Example
Program Output 1 2 3 4 5 6 7 8 9 10

8. What does the following program print?
#include <stdio.h> int main(){ int i,j=1; for (i=0;i<10;i+=2) { j++; printf("%d\n", j); } getchar(); j
For Loop Start 1
i = 0 2
i = 2 3
i = 4 4
i = 6 5
i = 8 6

9. while Repetition Statements
The format
Initialization (counter)
while (<testing> or <condition>) {
body for the loop (statements)
increment for the counter }
Example:
int counter = 1; // initialization
while ( counter <= 10 ) { // repetition condition
printf( "%d\n", counter );
++counter; // increment }
The statement
int counter = 1;
Names counter
Defines it to be an integer
Reserves space for it in memory
Sets it to an initial value of 1
5/22/2019
KIC/Introduction to Computer Programming

10. Example
Program Output 1 2 3 4 5 6 7 8 9 10

11. Comparison (While Loop Vs. For Loop)
If we want to display the numbers from 0 to 10 then both loop statements will be as below:
int count = 0;
while ( count < = 10 )
{ printf (“ \n %i ”, count);
count++; }
Initialization
Increment
int count;
for (count = 0; count < = 10; count++) {
printf (“ \n %i ”, count); }
5/22/2019
KIC/Introduction to Computer Programming

12. Comparison (While Loop Vs. For Loop)
Example
5/22/2019
KIC/Introduction to Computer Programming

13. do…while Repetition Statements
The format
Initialization (counter) do {
body for the loop (statements)
increment for the counter
} while (<testing> or <condition>); 1 2 3 4 5 6 7 8 9 10
Example
int count = 0; do {
printf (“ \n %d ”, count);
count++; or count=count+1;
} while (count<=10);
5/22/2019
KIC/Introduction to Computer Programming

14. Example

15. Comparison (While Loop Vs. do.. While Loop)
5/22/2019
KIC/Introduction to Computer Programming

16. KIC/Introduction to Computer Programming
Questions ( (6
Describe what happens in the following loop:
int d=7
int c=2
while(c!=d){
c=c+2;}
5/22/2019
KIC/Introduction to Computer Programming