C Exercises: Calculate the sum of numbers from 1 to n

Last update on August 07 2025 12:51:32 (UTC/GMT +8 hours)

2. Sum of Numbers Recursively Variants

Write a program in C to calculate the sum of numbers from 1 to n using recursion.

Pictorial Presentation:

C Exercises: Calculate the sum of numbers from 1 to n

Sample Solution:

C Code:

#include<stdio.h>
 
int sumOfRange(int);
 
int main() 
{
   int n1;
   int sum;
	printf("\n\n Recursion : calculate the sum of numbers from 1 to n :\n");
	printf("-----------------------------------------------------------\n");    
 
   printf(" Input the last number of the range starting from 1 : ");
   scanf("%d", &n1);
 
   sum = sumOfRange(n1); 
   printf("\n The sum of numbers from 1 to %d : %d\n\n", n1, sum);
 
   return (0);
}
 
int sumOfRange(int n1) 
{
   int res;
   if (n1 == 1) 
   {
      return (1);
   } else 
   {
      res = n1 + sumOfRange(n1 - 1); //calling the function sumOfRange itself
   }
   return (res);
}

Sample Output:

 Recursion : calculate the sum of numbers from 1 to n :                                                       
-----------------------------------------------------------                                                   
 Input the last number of the range starting from 1 : 5                                                       
                                                                                                              
 The sum of numbers from 1 to 5 : 15

Explanation:

int sumOfRange(int n1) 
{
   int res;
   if (n1 == 1) 
   {
      return (1);
   } else 
   {
      res = n1 + sumOfRange(n1 - 1); //calling the function sumOfRange itself
   }
   return (res);
}

The above function sumOfRange() calculates the sum of all natural numbers from 1 to the given number n1. It uses a recursive approach to calculate the sum, where if the number n1 is 1, the function returns 1, otherwise it adds n1 to the sum of all natural numbers from 1 to n1-1 and returns the result.

Time complexity and space complexity:

The time complexity of this function is O(n), where n is the given input number n1. This is because the function makes n recursive calls, each with a constant time complexity of O(1).

The space complexity of this function is also O(n), because the function creates n activation records on the call stack, one for each recursive call.

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to calculate the product of numbers from 1 to n using recursion.
Write a C program to compute the sum of squares of numbers from 1 to n recursively.
Write a C program to generate a cumulative sum array from 1 to n using recursion and print the intermediate sums.
Write a C program to calculate the sum of all even numbers from 1 to n using recursion.

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C Programming Code Editor:

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