The below program will accept the number “n” from the user and calculates the sum of first “n” natural numbers.

For example, if the input provided by the user is 5 then it will calculate the sum of first 5 natural numbers i.e., 1+2+3+4+5

/*
Program Name: Program in C++ to find sum of first "n" natural numbers
Author: LearnCPPOnline.com
*/

#include 
#include "conio.h"
using namespace std;

void main() 
{

	int sum, digit, n;

	sum = 0;
	digit = 1;
	
	cout << "Enter a number n: "; cin >> n;

	while(digit <= n)
	{
		sum = sum + digit;
		digit++;
	}

	cout << "Sum of first " << n << " natural numbers: " << sum << endl;
	getch();

}

Output

Enter a number n: 10
Sum of first 10 natural numbers: 55

Note: The above program is written and tested using Microsoft Visual Studio 2008