Q:

Error "system" is ambiguous?

I have a simple program, and it works fine, but the system("CLS"); and system("pause"); statements have red IntelliSense lines underneath them. When I move my cursor over them it says Error "system" is ambiguous. What is causing that?
Here is my code:
#include <iostream>
#include <cmath>
using namespace std;

int main()
{
  int choice = 0;
  const double PI = 3.14159;
  double sideSquare = 0.0;
  double radius = 0.0;
  double base = 0.0;
  double height = 0.0;

  cout << "This program calculates areas of 3 different objects." << endl;
  cout << "1.) Square" << endl;
  cout << "2.) Circle" << endl;
  cout << "3.) Right Triangle" << endl;
  cout << "4.) Terminate Program" << endl << endl;

  cout << "Please [Enter] your object of choice: ";
  cin >> choice;
  system("CLS"); // The problem is here...

  switch(choice)
  {
   case 1: 
    cout << "Please [Enter] the length of the side of the square: ";
    cin >> sideSquare;
    cout << "The area is: " << pow(sideSquare, 2) << endl;
    break;

   case 2: 
    cout << "Please [Enter] the radius of the circle: ";
    cin >> radius;
    cout << "The area is: " << PI * pow(radius, 2) << endl;
    break;

    case 3:
    cout << "Please [Enter] the base of the triangle: ";
    cin >> base;
    cout << endl << "Now [Enter] the height of the triangle: ";
    cin >> height;
    cout << "The area is: " << (base * height) / 2 << endl;
    break;

  default:
    cout << "Please [Enter] a valid selection next time." << endl;
    return 0;
  }
  system("pause"); // ... and here.
  return 0;
}

A:

You need to #include <cstdlib>
Source: http://en.cppreference.com/w/cpp/utility/program/system
Also, try to avoid system, it's dangerous.  To pause the program when it's finished, put a breakpoint on the } at the end of main.  There isn't a standard way to clear the screen unfortunately.
For future reference, the red squiggles are intellisense errors, which are shown by a different front-end than the one that actually compiles the code, so the red squiggles are sometimes wrong, especially with complex templates.  In most cases, including this one, it's correct though.

