C Programming for Loop

C Programming Loops

Loops cause program to execute the certain block of code repeatedly until test condition is false. Loops are used in performing repetitive task in programming. Consider these scenarios:

  • You want to execute some code/s 100 times.
  • You want to execute some code/s certain number of times depending upon input from user.

These types of task can be solved in programming using loops.

There are 3 types of loops in C programming:

  1. for loop
  2. while loop
  3. do...while loop

for Loop Syntax

for(initialization statement; test expression; update statement) {
       code/s to be executed; 
}

How for loop works in C programming?

The initialization statement is executed only once at the beginning of the for loop. Then the test expression is checked by the program. If the test expression is false, for loop is terminated. But if test expression is true then the code/s inside body of for loop is executed and then update expression is updated. This process repeats until test expression is false.

This flowchart describes the working of for loop in C programming.

Flowchart of for loop in C programming language

for loop example

Write a program to find the sum of first n natural numbers where n is entered by user. Note: 1,2,3... are called natural numbers.

 
#include <stdio.h>
int main(){
    int n, count, sum=0;
    printf("Enter the value of n.\n");
    scanf("%d",&n);
    for(count=1;count<=n;++count)  //for loop terminates if count>n
    {
        sum+=count;    /* this statement is equivalent to sum=sum+count */
    }
    printf("Sum=%d",sum);
    return 0;
}

Output

Enter the value of n.
19
Sum=190

In this program, the user is asked to enter the value of n. Suppose you entered 19 then,  count is initialized to 1 at first. Then, the test expression in the for loop,i.e.,  (count<= n) becomes true. So, the code in the body of for loop is executed which makes sum to 1. Then, the expression ++count is executed and again the test expression is checked, which becomes true. Again, the body of for loop is executed which makes sum to 3 and this process continues. When count is 20, the test condition becomes false and the for loop is terminated.

C for Loop Examples

Note: Initial, test and update expressions are separated by semicolon(;).