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