Loop Statements in C

Girdhar Gopal Singh  Print 
09 Aug 2018
28 Oct 2018
Intermediate
1.78K

Loops are used to repeat a block of statements for a certain time. C language offers three types of loops - while, do-while and for loops for iterating a set of statements.

While

This loop executes a statement or a block of statements until the specified boolean expression evaluates to false.

#include<stdio.h>
#include<conio.h>
void main()
{
 clrscr();
 int number = 5;
 while (number != 0) //specified boolean expression
 {
 printf("Current value of n is %d", number);
 number--; //update statement 
 }
 getch();
}
/* Output:
 Current value of n is 5
 Current value of n is 4
 Current value of n is 3
 Current value of n is 2
 Current value of n is 1
*/

Important Note

Typically, while loop is useful when you are not aware of exact number of iterations.

Do-While Loop

This loop executes a statement or a block of statements until the specified boolean expression evaluates to false.

#include<stdio.h>
#include<conio.h>
void main()
{
 clrscr();
 char choice = 'Y';
 do
 {
 int number = 5;

 printf("\nPrint Number : %d", number);

 printf("\nDo you want to continue (y/n) :");
 scanf("%c",&choice);

 } while (choice == 'y'); //specified boolean expression

 getch(); 
}
/*
 Output:
 Print Number : 5
 Do you want to continue (Y/N) :y

 Print Number : 5
 Do you want to continue (Y/N) :n
*/

Important Note

Typically, while loop is useful when you are not aware of exact number of iterations.

For Loop

This loop has three sections - index declaration, condition (boolean expression) and updation section. In each for loop iteration, the index is updated (incremented/decremented) by updating section and checked with the condition. If the condition is matched, it continues execution until the specified boolean expression evaluates to false.

#include<stdio.h>
#include<conio.h>
int main()
{
clrscr();
 int a,f,i;
 printf("Enter a number: ");
 scanf("%d",&a);
 f=1;
 for(i=1;i<=a;i++)
 f = f * i;
 printf("Factorial: %d",f);
getch();
}
/*
Output:
Enter a number:5
Factorial:120
Enter a number:4
Factorial:24
*/

Important Note

Typically, for loop is useful when you are aware of exact number of iterations. Normally, it is used for iterating over arrays and for sequential processing.

While, Do..While and For Loop

A program can be build by using one of the loop statement. For example, we can print numbers from 1 to 100 using all loops.

While Loop example
int i=0;
while(i<100)
 {
 i++;
 printf("%d\n", i);
 }
Do While Loop example
 int i=0;
 do
 {
 i++;
 printf("%d\n",i);
 }while(i<100);
For Loop example
 for(int i = 1; i <= 100; i++)
 {
 printf("%d\n", i);
 }

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