C program to find sum of natural numbers from 1 to n

Categories C programming 2 mins read

Write a C program to find the sum of all natural numbers between 1 to n using for loop. How to find sum of natural numbers in a given range in C programming. Logic to find sum of all natural numbers in a given range in C programming.

Example

Input

Input upper limit: 10

Output

Sum of natural numbers 1-10: 55

Required knowledge

Basic C programming, Relational operators, For loop

Logic to find sum of natural numbers from 1 to n

Step by step descriptive logic to find sum of n natural numbers.

  1. Input upper limit to find sum of natural numbers. Store it in some variable say N.
  2. Initialize another variable to store sum of numbers say sum = 0.
  3. In order to find sum we need to iterate through all natural numbers between 1 to n. Initialize a loop from 1 to N, increment loop counter by 1 for each iteration. The loop structure should look like for(i=1; i<=N; i++).
  4. Inside the loop add previous value of sum with i. Which is sum = sum + i.
  5. Finally after loop print the value of sum.

Program to find sum of natural numbers from 1 to n

/**
 * C program to find sum of natural numbers between 1 to n
 */

#include <stdio.h>

int main()
{
    int i, n, sum=0;

    /* Input upper limit from user */
    printf("Enter upper limit: ");
    scanf("%d", &n);

    /* Find sum of all numbers */
    for(i=1; i<=n; i++)
    {
        sum += i;
    }

    printf("Sum of first %d natural numbers = %d", n, sum);

    return 0;
}

Note: In above program I have used shorthand assignment operator sum += i which is equivalent to sum = sum + i.

Output

Enter upper limit: 10
Sum of first 10 natural numbers = 55

Program to find sum of natural numbers in given range

/**
 * C program to find sum of natural numbers in given range
 */

#include <stdio.h>

int main()
{
    int i, start, end, sum=0;

    /* Input lower and upper limit from user */
    printf("Enter lower limit: ");
    scanf("%d", &start);
    printf("Enter upper limit: ");
    scanf("%d", &end);

    /* Find sum of all numbers */
    for(i=start; i<=end; i++)
    {
        sum += i;
    }

    printf("Sum of natural numbers from %d to %d = %d", start, end, sum);

    return 0;
}

Output

Enter lower limit: 10
Enter upper limit: 15
Sum of natural numbers from 10 to 15 = 75

Happy coding 😉