01: #include <iostream>
02: #include <cmath>
03: using namespace std;
04: 
05: int main()
06: {  double area;
07:    cout << "Please enter the area of a square: ";
08:    cin >> area;
09:    if (area < 0)
10:    {  cout << "Error: Negative area.\n";
11:       return 1;
12:    }
13: 
14:    /* now we know that area is >= 0  */
15:    double length = sqrt(area);
16:    cout << "The side length of the square is " 
17:         << length << "\n";
18: 
19:    return 0;
20: }