The document discusses while, do-while, and for loops in C programming. It provides examples of using each loop type to iterate through a sequence and print or calculate values. Key differences are highlighted, such as how the while loop checks the condition first before iterating, while do-while always executes the body at least once before checking the condition. Both for and do-while loops can mimic the functionality of each other through minor syntactic differences.

3. Abu Mohammad Musa
Md. Mahbub Morshed Chowdhury
S.M.Zahidul Islam

4. while (test expression)
{
statement to be executed.
}
The while loop checks whether the test expression is true or not. If it is true, code/s
inside the body of while loop is executed, that is, code/s inside the braces { } are
executed. Then again the test expression is checked whether test expression is true
or not. This process continues until the test expression becomes false

5. Example
#include<stdio.h>
int main ()
{
char ch;
printf("Enter any character: n");
while (ch!='q' && ch!='Q')
{
scanf("%c",&ch);
}
printf("nFound the Q");
return 0;
}

7. Write a C program to find the factorial of a number, where the number is entered by user. (Hints: factorial of n = 1*2*3*...*n
#include <stdio.h>
int main()
{
int number,factorial;
printf("Enter a number.n");
scanf("%d",&number);
factorial=1;
while (number>0) /* while loop continues util test
condition number>0 is true */
{
factorial=factorial*number;
--number;
}
printf("Factorial=%d",factorial);
return 0;
}
Output
Enter a number.
5
Factorial=120

8. Example
#include<stdio.h>
int main ()
{
int x,a,b;
x=10;
a=5;
b=15;
printf("--xt--at--bn");
printf("-------------------n");
while(--a,--b,--x)
{
printf("%dt%dt%dn",x,a,b);
}
return 0;
}
Output

9. do...while loop
In C, do...while loop is very similar to while loop. Only difference between these two loops is that, in while
loops, test expression is checked at first but, in do...while loop code is executed at first then the condition is
checked. So, the code are executed at least once in do...while loops.
Do
{
some code/s;
}
while (test expression);

10. Example
#include<stdio.h>
int main ()
{
int a,b;
char ch;
printf("Do you want to:n");
printf("Add, Subtraction, Multiply or
Divide?n");
do
{
printf("nEnter first letter: n");
scanf("%c",&ch);
}
while(ch!='A' && ch!='S' && ch!='M'
&& ch!='D');
printf("n");
printf("Enter the first number: n");
scanf("%d",&a);
printf("Enter second number: n");
scanf("%d",&b);
if(ch=='A')
printf("n%d",a+b);
else if(ch=='B')
printf("n%d",a-b);
else if(ch=='M')
printf("n%d",a*b);
else if(ch=='D')
printf("n%d",a/b);
return 0;
}
Output

11. Example 2
#include<stdio.h>
int main()
{
int i=10;
do
{
printf("%dn",i);
i=i-1;
if(i==6)
{
break;
}
}
while(i>0);
return 0;
}
Output

12. At first codes inside body of do is executed. Then, the test expression is checked. If it is true, code/s inside body of do
are executed again and the process continues until test expression becomes false(zero).
Notice, there is semicolon in the end of while (); in do...while loop.

13. Write a C program to add all the numbers entered by a user until user enters 0.
#include <stdio.h>
int main(){
int sum=0,num;
do
{
printf("Enter a numbern");
scanf("%d",&num);
sum+=num;
}
while(num!=0);
printf("sum=%d",sum);
return 0;
}
Output
Enter a number
3
Enter a number
-2
Enter a number
0
sum=1
In this C program, user is asked a number and it is added with sum. Then, only the test condition in the do...while loop is
checked. If the test condition is true,i.e, num is not equal to 0, the body of do...while loop is again executed until num
equals to zero.

14. Similarity between for and do while loop
Syntax of for loop
do .. While loop does the same thing as for loop does
But the for loop is compact and easy to use.

15. #include<stdio.h>
int main()
{
int i;
for(i=1;i<=5;i++)
{
printf("%d",i);
}
return 0;
}
This program shows the same output but they are
written in for loop and do while loop
Output
12345
Output
12345
#include<stdio.h>
int main()
{
int i=1;
do
{
printf("%d",i);
i++;
}
while (i<=5);
return 0;
}