C Sum of Natural Numbers Program

In this tutorial, you will learn how to write a C++ Program to find the sum of natural numbers using formula, or a loop statement.

C Sum of Natural Numbers

To find the sum of first n natural numbers in C++, we can use the for loop to iterate from 1 to n and accumulate the sum, or we can also use the formula n(n+1)/2 directly.

In this tutorial, we will write C++ Programs to find the sum of natural numbers, with the two methods mentioned above.

Programs

1 Compute sum of natural numbers using For loop

In the following program, we read a number into n, and find the sum of natural numbers from 1 to n, using For Loop.

main.cpp

#include <iostream>
using namespace std;

int main() {
    int n;
    cout << "Enter a number  : ";
    cin >> n;
    
    int sum = 0;
    for(int i = 1; i <= n; i++) {
        sum += i;
    }
    
    cout << "Sum : " << sum << endl;
}

Output

Enter a number  : 5
Sum : 15
Program ended with exit code: 0

Enter a number  : 1256
Sum : 789396
Program ended with exit code: 0

2 Compute sum of natural numbers using formula

In the following program, we read a number into n, and find the sum of natural numbers from 1 to n, using the formula n(n+1)/2.

main.cpp

#include <iostream>
using namespace std;

int main() {
    int n;
    cout << "Enter a number  : ";
    cin >> n;
    
    int sum = n * (n + 1) / 2;
    cout << "Sum : " << sum << endl;
}

Output

Enter a number  : 5
Sum : 15
Program ended with exit code: 0

Enter a number  : 1256
Sum : 789396
Program ended with exit code: 0

Conclusion

In this C++ Tutorial, we learned how to find the sum of first n Natural Numbers.