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

## C Recursion : Exercise-2 with Solution

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

**Pictorial Presentation:**

**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: **

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