C Program to Find the Sum of First N Natural Numbers

• Write a c program to find sum of N numbers.

In this program, user first enters the count of integers that he wants to add. Then we take N integers as input from user using scanf function inside a for loop and keep on adding it to a variable sum. Once user finished entering N integers we print sum of all N integers on screen. Here we are using addition arithmetic operator(‘+’) to add numbers.

Check this tutorial for detailed explanation of Arithmetic operators.

C program to calculate sum of N numbers using for loop and without using array

/*
* C Program to add N numbers
*/
#include <stdio.h>
#include <conio.h>
 
int main(){
      
    int numberCount=0, number, counter, sum=0;
     
    printf("Enter the number of integers to add: ");
    scanf("%d",&numberCount);
     
    printf("Enter %d numbers seperated by space \n", numberCount);
    for(counter = 0; counter < numberCount; counter++){
        scanf("%d", &number);
        sum = sum + number;
    }
    printf("SUM = %d", sum);
    getch();
    return 0;
}

Program Output

Enter the number of integers to add: 5
Enter 5 numbers seperated by space 
1 2 3 4 5
SUM = 15

C program to calculate sum of N numbers using array

In this program we first store all the numbers entered by user in an integer array. Then we traverse this array from index 0 to N-1 and add all numbers using a for loop and ‘+’ operator. In line number 21, we can also uses shorthand assignment operators ‘+=’ for addition. Check this tutorial for detailed explanation of Shorthand assignment operators.

/*
* C Program to add N numbers using Array
*/
#include <stdio.h>
#include <conio.h>
 
int main(){
    /* Using array of size 500 to store input numbers */
    int numberCount=0, numbers[500], counter, sum=0;
     
    printf("Enter the number of integers to add: ");
    scanf("%d",&numberCount);
     
    /* Read numberCount numbers from user and store it in array numbers*/
    printf("Enter %d numbers seperated by space \n", numberCount);
    for(counter = 0; counter < numberCount; counter++){
        scanf("%d", &numbers[counter]);
    }
    /* Add all number in array from index 0 to numberCount-1 */
    for(counter = 0; counter < numberCount; counter++){
        sum = sum + numbers[counter];
    }
     
    printf("SUM = %d", sum);
    getch();
    return 0;
}

Program Output

Enter the number of integers to add: 7
Enter 5 numbers seperated by space 
7 6 5 4 3 2 1
SUM = 28

C program to calculate sum of N numbers using recursion

We can use recursion to find sum of N numbers by breaking a problem into smaller problem. Function “getSum(int numberCount)” takes numberCount numbers as input and adds them recursively and returns the result to calling function.

/*
* C Program to add N numbers using Recursion
*/
#include <stdio.h>
#include <conio.h>
  
int getSum(int numberCount);
  
int main(){
      
    int numberCount=0, number, counter, sum=0;
    
    printf("Enter the number of integers to add: ");
    scanf("%d",&numberCount);
    
    printf("Enter %d numbers seperated by space \n", numberCount);
    sum = getSum(numberCount);
    printf("SUM = %d", sum);
    
    getch();
    return 0;
}
  
/*
* Function to return sum of N numbers
*/
int getSum(int numberCount){
    int sum=0;
    /*  exit condition */
    if(0 == numberCount)
        return 0;
    scanf("%d", &sum);
    /* Recursively call getSum by reducing numberCount by 1 */
    return sum + getSum(numberCount - 1);
}