# 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:

- Natural numbers: These numbers are counting numbers; positive integers beginning with 1 and increasing by 1 forever. eg:1,2,3,4….
- Using loops in C.
- Header files in C.

### 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; }

OutputEnter 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.

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