In this example, you'll learn to calculate the sum of natural numbers.

To understand this example, you should have the knowledge of the following C++ programming topics:

Positive integers 1, 2, 3, 4... are known as natural numbers.

This program takes a positive integer from user( suppose user entered `n` ) then, this program displays the value of 1+2+3+....+n.

```
#include <iostream>
using namespace std;
int main()
{
int n, sum = 0;
cout << "Enter a positive integer: ";
cin >> n;
for (int i = 1; i <= n; ++i) {
sum += i;
}
cout << "Sum = " << sum;
return 0;
}
```

**Output**

Enter a positive integer: 50 Sum = 1275

This program assumes that user always enters positive number.

If user enters negative number, **Sum = 0** is displayed and program is terminated.

This program can also be done using recursion. Check out this article for calculating sum of natural numbers using recursion.