C++ Midpoint Rule (Rectangle Method)

Implementation of Midpoint Rule (Rectangle Method) (Integral Approximation) written in C++.

Enter begining of interval: -2
Enter end of interval: 2
Enter number of iterations: 1000000
Integral is equal to: 5.33333

#include <iostream>

// ? 2018 TheFlyingKeyboard and released under MIT License 
// theflyingkeyboard.net

using namespace std;

double function(double x);

int main() {
  double intervalBegin;
  double intervalEnd;
  int count;
  double integral = 0;
  double step;

  cout << "Enter begining of interval: ";
  cin >> intervalBegin;

  cout << "Enter end of interval: ";
  cin >> intervalEnd;

  cout << "Enter number of iterations: ";
  cin >> count;

  step = (intervalEnd - intervalBegin) / count;

  for (int i = 1; i <= count; ++i) {
    integral += step * function(intervalBegin + (i - 1) * step);
  }

  cout << "Integral is equal to: " << integral << endl;

  int a;
  cin >> a;
  return 0;
}

double function(double x) {
  return x * x;
}