## Introduction

This program is used to calculate the sum of the first ‘n’ natural numbers, where n is any value up to where the user wishes to calculate the sum.

To understand this program, you must have gone through the following concepts of C++ programming

1. while loop

2. operators

Go through the article on ‘for’ loop written in the C++ language series to get a better understanding.

The positive numbers that start from 1 are known as Natural numbers.

The sum begins from 1 since natural numbers start from 1.

The main purpose of writing the same program in different ways is to make the learners aware of differences in various loops like **for** loop and **while**.

## Program

#include<iostream> using namespace std; int main() { int num; // num is the value up to where the sum is calculated cout<<"Enter a positive integer: "; cin>>num; int sum=0; int i=1; // initialization while(i<=num) // condition { sum=sum+i; i++; // increment } cout<<"Sum: "<<sum; return 0; }

## Output

## Explanation

**int num;**

‘num’ is the variable declared to store the value up to where the user wishes to calculate the sum.

**cout<<“Enter a positive integer: “;**

**cin>>num;**

Using cout and cin statements, we take input from the user.

**int sum=0;**

A new variable is declared and initialized with a 0 value to store the sum of natural numbers.

**int i=1;**

The iterator ‘i’ is initialized with a 0 value.

**while(i<=num)**

The while loop starts here with a condition, and it will iterate until the condition gives a false result.

**sum=sum+i;**

In each iteration, the value of ‘i’ is added to ‘sum’.

**i++;**

After that, the value of ‘i’ is incremented by 1.

When the condition in the while loop becomes false, the loop gets terminated, and the final value of the ‘sum’ is printed.

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