# C Program to Find the Sum of First N Natural Numbers

## Sum of Natural Numbers in C

In this article, we will see C Program to Find the Sum of First N Natural Numbers. A Natural number is the same as a Counting number. They are used to Count the number of real physical objects. Natural numbers start from 1 and go on infinite.

```The positive numbers 1,2,3 ... are known as natural numbers.

Formula for Sum of First n natural numbers is : n(n+1)/2.
If you want to add first 5 Natural number
then we find the Sum of 1+2+3+4+5 =15.``` ## What we will learn

• Method 1: Iterative way
• Method 2: Direct Formula
• Method 3: Recursive Approach

## Method 1

For an input n

• Create variable sum = 0
• Run a for loop in iteration (I) from 1 -> n
• Each time adding I to sum
• Print the sum value after the loop terminates

### Code

Run
```#include <stdio.h>

int main()
{
int n;
scanf("%d",&n);

int sum = 0;

for(int i=1;i<=n;i++)
// is same as writing sum = sum + i
sum += i;

printf("Sum is %d",sum);

return 0;
}

// Time complexity : O(n)
// Space complexity : O(1)
```

```5
Sum is 15
```

## Method 2

For an input n

• Create variable sum = 0
• Use formula sum =  n(n+1)/2
• Print the sum value

### Code

Run
```#include <stdio.h>

int main()
{
int n;
scanf("%d",&n);

int sum = n*(n+1)/2;

printf("The sum is %d",sum);

return 0;
}
// Time complexity : O(1)
// Space complexity : O(1)
```

```6
Sum is 21
```

## Method 3

For an input n

• Create variable sum = 0
• Call function getSum(sum, n)
• Base Case, n == 0 return sum
• Others return n + getSum(sum, n-1)
• Print the sum value in main

### Code

Run
```#include <stdio.h>

int getSum(int sum,int n)
{
if(n==0)
return sum;

return n+getSum(sum,n-1);
}

int main()
{
int n, sum = 0;
scanf("%d",&n);

printf("%d",getSum(sum, n));

return 0;
}
// Time complexity : O(n)
// Space complexity : O(1)
// Auxilary space complexity : O(N)
// Due to function call stack
```

```5
Sum is 15
```

### Related Banners

Get PrepInsta Prime & get Access to all 150+ courses offered by PrepInsta in One Subscription