#include <iostream>
#include <string>
using namespace std;

int main()
{
    // int double float char <== built-in data types
    //                           (primitive data types)
    //                     i.e. built-in to the C++ language
//    char user_input;

    string user_input;
    cout << "Enter either 'fahr' or 'celsius': ";
    cin >> user_input;

    double fahr, celsius;

    // boolean data type -- true (non-zero), false (0)
    bool is_user_input_valid = false;

    if ( user_input == "fahr"  ||  user_input == "fahrenheit"  ||
         user_input == "f" )
    {
        is_user_input_valid = true;
        cout << "Please enter Fahrenheit value: ";
        cin >> fahr;
        celsius = ( fahr - 32 ) * ( 5.0 / 9.0 );
        cout << "Converted to Centigrade: " << celsius << endl;
    }
    else if ( user_input == "celsius" )
    {
        is_user_input_valid = true;
        cout << "Please enter Centigrade value: ";
        cin >> celsius;
        fahr = ( 9.0 / 5.0 ) * celsius + 32;
        cout << "Converted to Fahrenheit: " << fahr << endl;
    }
    else
    {
        is_user_input_valid = false;
//        cout << "Can't you read directions???" << endl;
        cerr << "Can't you read directions???" << endl;

//        return -1;  // exit the program
    }


    if ( is_user_input_valid )
    {
        // if we're inside this if statement, then
        //  the user typed in a valid string to begin with....

        if ( fahr == 32 )
        {
            cout << "Pure water freezes at this temperature.\n";
        }
	// etc.
    }


    return 0;
}