C Program to Find Sum of N Numbers using Recursion

This is a C program to find sum of first N numbers using recursion.

Problem Description

The following C program using recursion displays the first N natural number on the terminal.

Problem Solution

The user enters the Nth number as the input, the program then calculates the sum of first N numbers using recursion and then displays the final result.

Program/Source Code

#include <stdio.h>
 
void display_sum(int);
 
int main()
{
    int num;
 
    printf("Enter the Nth number: ");
    scanf("%d", &num);
    display_sum(num);
    return 0;
}
 
void display_sum(int num)
{
    static int sum = 0;
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This is a C program to find sum of first N numbers using recursion.

Problem Description

The following C program using recursion displays the first N natural number on the terminal.

Problem Solution

The user enters the Nth number as the input, the program then calculates the sum of first N numbers using recursion and then displays the final result.

Program/Source Code

#include 
 
void display_sum(int);
 
int main()
{
    int num;
 
    printf("Enter the Nth number: ");
    scanf("%d", &num);
    display_sum(num);
    return 0;
}
 
void display_sum(int num)
{
    static int sum = 0;
 
    if (num == 0)
    {
        printf("Sum of first N numbers is %d\n", sum);
        return;
    }
    else
    {
        sum += num;
        display_sum(--num);
    }
}

Program Explanation

In this C program, we are reading the integer number using the num variable. To find Sum of N Numbers using Recursion, call the display_sum() by passing the num variable value as argument.

In function display_sum(), initialize the value of sum variable with 0 value. Here, sum variable is defined as static so that only one copy of that object will be there upon repeated invocation of that function. If else conditional statement is used to check the value of num variable. If the value of num variable is non zero, we will increment the value of sum variable by num and then call display_sum() recursively by reducing the value of num variable by 1.

Once num becomes 0, we know that we have completed the recursion and we will display the final result stored in the sum variable.

Output:

Enter the Nth number: 3

Sum of first N numbers is 6

 

Enter the Nth number: 5

Sum of first N numbers is 15