While loop is also known as a pre-tested loop. In general, a while loop allows a part of the code to be executed multiple times depending upon a given boolean condition. It can be viewed as a repeating if statement. The while loop is mostly used in the case where the number of iterations is not known in advance.

Syntax of while loop in C language

The syntax of while loop in c language is given below:

1. while(condition){  
2. //code to be executed  
3. }  

Flowchart of while loop in C

Example of the while loop in C language

Let's see the simple program of while loop that prints table of 1.

1. #include<stdio.h>  
2. int main(){    
3. int i=1;      
4. while(i<=10){      
5. printf("%d \n",i);      
6. i++;      
7. }  
8. return 0;  
9. }    

Output

1
2
3
4
5
6
7
8
9
10

Program to print table for the given number using while loop in C

1. #include<stdio.h>  
2. int main(){    
3. int i=1,number=0,b=9;    
4. printf("Enter a number: ");    
5. scanf("%d",&number);    
6. while(i<=10){    
7. printf("%d \n",(number*i));    
8. i++;    
9. }    
10. return 0;  
11. }   

Output

Enter a number: 50
50
100
150
200
250
300
350
400
450
500

Enter a number: 100
100
200
300
400
500
600
700
800
900
1000

Properties of while loop

• A conditional expression is used to check the condition. The statements defined inside the while loop will repeatedly execute until the given condition fails.
• The condition will be true if it returns 0. The condition will be false if it returns any non-zero number.
• In while loop, the condition expression is compulsory.
• Running a while loop without a body is possible.
• We can have more than one conditional expression in while loop.
• If the loop body contains only one statement, then the braces are optional.

Example 1

1. #include<stdio.h>  
2. void main ()  
3. {  
4.     int j = 1;  
5.     while(j+=2,j<=10)  
6.     {  
7.         printf("%d ",j);   
8.     }  
9.     printf("%d",j);  
10. }  

Output

3 5 7 9 11

Example 2

1. #include<stdio.h>  
2. void main ()  
3. {  
4.     while()  
5.     {  
6.         printf("hello Javatpoint");   
7.     }  
8. }  

Output

compile time error: while loop can't be empty	

Example 3

1. #include<stdio.h>  
2. void main ()  
3. {  
4.     int x = 10, y = 2;  
5.     while(x+y-1)  
6.     {  
7.         printf("%d %d",x--,y--);  
8.     }  
9. }  

Output

infinite loop 

Infinitive while loop in C

If the expression passed in while loop results in any non-zero value then the loop will run the infinite number of times.

1. while(1){  
2. //statement  
3. }