C Program for Sum of First N Natural Numbers

The program adds first N natural numbers (starts from 1) and prints the sum in the console. We wrote this program using Dev C++ version 4.9.9.2 on a Windows 7 64-bit system.  You may try other standard C compilers to run the program with modifications.

Learn following c programming concepts before you attempt this example program.

• C Assignment Operators
• C Arithmetic Operators
• C Reading Input Values
• C Printing Output Values
• C For Loop

Problem Definition

Natural numbers are all positive numbers greater than number 0 and it does not include the number zero.

For example

Natural numbers …

This C program reads the value of number N which is a natural number and then sum all other natural numbers up to number N start from 1. Suppose then

Sum 

Flowchart – Sum of First N Natural Numbers

Program Code – Sum of First N Natural Numbers

/* Program for sum of First N Natural Numbers */ 
#include <stdio.h>
#include <stdlib.h> 
main() {     
int num,i,sum;
    sum = 0; /* read the number */     
    printf("Enter number to sum:");
    scanf("%d",&num);     
    for(i=1;i<=num;i++)     {         
    sum = sum + i;     
}     
printf("sum of %d number is %d\n",num,sum);     
    getch();
    return 0; }

The most important piece of code in the above example is the for loop.