C++ Program to Calculate Sum of Natural Numbers

Natural Numbers

• THe Natural Numbers are the positive integers starting from 1.
• Positive integers 1, 2, 3, 4... are known as natural numbers.
• The 1st program already initialized the number to the variable.
• The 2nd program takes a positive integer from user( suppose user entered n ) then, this program displays the value of 1+2+3+....+n.

Example 1: Program to Find Sum of Natural Numbers using For loop.

// calculate the sum of natural numbers using for loop
#include <iostream>
using namespace std;
  
int main()
{
    int n=5, sum = 0, i;
    for (i = 1; i <= n; i++) {
        sum += i;
    }

    cout <<"Sum of First" << n << "Natural Numbers is " << sum;
    return 0;
}

Output

Sum of First 5 Natural Numbers is 15

Working

• In This program, a For loop is run from 1 to n.
• In each itreration of the loop, the value of i is added to the sum.
• So, the sum of the first n natural numbers is obtained.

Example 2: Program to Find Sum of Natural Numbers using For loop.

// calculate the sum of natural numbers using for loop
// Number Entered By User
#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: 10
Sum = 55

Working

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.

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