PA 6 - readDouble

// Christian Ballard
// COSC 1336 - 001
// This program should validate user input for doubles.
// Febuary 9, 2015
#include<iostream>
#include<string>
#include<limits>
#include<cctype>
using namespace std;

//Prototypes
double readDouble(string errorMsg = "", int min = INT_MIN, int max = INT_MAX);

int main()
{
    double x;
    do   {
            cout << " Enter a value: ";
            x = readDouble("test1 use default args");
            cout << " Enter a value: ";
            x = readDouble("test2 1.5,19.5", 1.5, 19.5);
            cout << " Enter a value: ";
            x = readDouble("test3 -2000.5678912,100.567", -2000.5678912, 100.567);
            cout << " Enter a value: ";
            x = readDouble("test4 -9999999,9999999", -9999999, 9999999);
            cout << " Enter a value: ";
            x = readDouble("test5 -929999999.5,929999999.5", -929999999.5, 929999999.5);
            cout << " Enter a value: ";
            x = readDouble("test6 -1,1234567890, default max", -1, 1234567890);
            cout << " Enter a value: ";
            x = readDouble("test7 -1234567890, 100", -1234567890, 100);
            cout << " Enter a value: ";
            x = readDouble("test8 -1234567890,1234567890", -1234567890, 1234567890);
            // etc.
    } while(true);



    system("pause");
    return 0;
}

double readDouble(string errorMsg, int min, int max)
{
    double someDouble;      // Stores each double entered.
    bool valid = false;     // Loop control flag indeicating validdity of entry
                            // initially assuming not valid.
    do
    {
        // Read an integer delimited by a whitespace character.
        cin >> someDouble;

        // Valid if within min to max range.
        valid = someDouble >= min && someDouble <= max;

        // Detect and remove invalid input.
        if (cin.fail() || !valid || !isspace(cin.peek()))
        {
            cout << "\nError! Invalid input.\n" << errorMsg << " must be a whole "
                << "number between " << min << " and " << max << ". \nTry Again: ";

            cin.clear();        // Clears the fail state.

            // Remove up to max number of chars in input stream or up to '\n'.
            cin.ignore(numeric_limits<streamsize>::max(), '\n');

            valid = false;      // No valid entry has been read.
        }
    } while (!valid); // Loop again, prompting user to re-enter a valid integer.

    // When valid input received, remove from input stream up to 100 remaining
    // characters or until reaches the '\n' <ENTER> character.
    cin.ignore(100, '\n');

    return someDouble; // Returns a valid double to calling environment.
}