Program to calculate the series (1) + (1+2) + (1+2+3) + … + (1+2+3+4+…+n) in C++

C++ Program to calculate the series (1) + (1+2) + (1+2+3) + (1+2+3+4) + … + (1+2+3+4+…+n)

Given: The value of n is input from user and we find the sum of the series where i-th term is sum of first i natural numbers.

Example:

Input : n = 6

Output :

1 = 1

1 + 2 = 3

1 + 2 + 3 = 6

1 + 2 + 3 + 4 = 10

1 + 2 + 3 + 4 + 5 = 15

1 + 2 + 3 + 4 + 5 + 6 = 21

The sum of the above series is : 56

# Algorithm

Take input n from the user.
Start a loop from i = 1 to i <= n.
Inside the loop, calculate the sum for the ith term by adding all the numbers from 1 to i.
After the loop, print the total sum as the result.

Code:

#include <iostream>
using namespace std;

int main() {
  int i, j, n, sum, total = 0;
  cout << "Enter the value for nth term: ";
  cin >> n;
  for (i = 1; i <= n; i++) {
    sum = 0;
    for (j = 1; j <= i; j++) {
      total += j;
      sum += j;
      cout << j;
      if (j < i) {
        cout << "+";
      }
    }
    cout << " = " << sum << endl;
  }
  cout << "\nThe sum of the above series is: " << total << endl;
}

Output

Enter the value for nth term: 5
1 = 1
1+2 = 3
1+2+3 = 6
1+2+3+4 = 10
1+2+3+4+5 = 15

The sum of the above series is: 35