# C Program to find Sum of first ‘n’ Natural numbers

In this C programming example, We will see the program that calculates the sum of first ‘n’ natural numbers. Also, we will discuss the execution of the program.

## 1. Introduction

Helpful topics to understand the implementation of this program better are:

### 1.1. Sum of ‘N’ Natural numbers using loops

Let’s implement a simple c program to find the sum of first n natural numbers using loops. In this example, we will use a `while` loop, but it can easily be replaced by any other loop.

```#include <stdio.h>

void sumOfNaturalNumber_UsingLoop(long number)
{
long counter = 1, sum = 0;
while (counter <= number)
{
sum = sum + counter;
counter++;
}
printf("Sum of Natural Numbers from 1 to %ld is : %ld\n", number, sum);
}

int main()
{
long number;

printf("Enter the number :\n");
scanf("%ld", &number);

sumOfNaturalNumber_UsingLoop(number);
return 0;
}```
```Output
Enter the number :
10
Sum of Natural Numbers from 1 to 10 is : 55
```

## 2. Understanding the Program

• `counter` is the iterating element that goes from `1` to `number` in the while loop.
• In every iteration, the sum is incremented by the value of the counter.
• At last, print the required sum of first n natural numbers.

## 3. Sum of ‘N’ Natural numbers using formula

The time complexity for the example implemented above is O(n), but we can use a simple mathematical formula to find the sum of first n natural numbers in O(1) time complexity.

So the formula to find the sum of first n natural numbers is `(n * (n +1))/2`.

So let’s replace the method using loops by the new˘efficient method that uses the formula.

```void sumOfNaturalNumber_UsingFormula(long number)
{
long sum = (number * (number + 1)) / 2;
printf("Sum of Natural Numbers from 1 to %ld is : %ld\n", number, sum);
}```

## 3. Conclusion

In this C Programming example, we have discussed, how to find the sum of first ‘n’ natural numbers and a glimpse over its implementation.

Also for the example C programs please refer to C Programming Examples.

All examples are hosted on Github.

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