Zachary Stence

The sum of the squares of the first ten natural numbers is,

The square of the sum of the first ten natural numbers is,

Hence the difference between the sum of the squares of the first ten natural numbers and the square of the sum is 3025 − 385 = 2640.

Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum.

I first solved this problem October 8th, 2014 in my AP Computer Science class in highschool. I do not have the original code I wrote, but I have redone the solution and included it below.

This problem is perhaps the easiest one yet on ProjectEuler. I just wrote two functions that return the sum of the squares and the square of the sum of the first n natural numbers (sumOfSq and sqOfSum, respectively). Then I just called them with 100 as the argument, and output the difference.

#include <iostream>

int sumOfSq(int n) {
  int sum = 0;
  for (int i = 1; i <= n; i++) {
    sum += i * i;
  }
  return sum;
}

int sqOfSum(int n) {
  int sum = 0;
  for (int i = 1; i <= n; i++) {
    sum += i;
  }
  return sum * sum;
}

int main() {
  std::cout << sqOfSum(100) - sumOfSq(100) << std::endl;
}

Answer: 25164150