PA 4 - Input Validation

//Christian Ballard
//COSC 1336 - 001
//January 28, 2015
//This program should take the users input of three digits and display them separately
#include<iostream>
#include<string>
#include<limits>
#include<cctype>
using namespace std;

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

int main()
{

    int number; // Will store the three digit number the user enters.
    int n1, n2, n3; // Will store the extracted digits.
    int number2; // Will store the original user input because the original becomes altered.
    const int ZERO = 0; // Named constant for 0.

    cout << "Please enter a value between 1 and 999. Your may enter '0' to exit." << endl;

    number = readInt("The Number", 0, 999);

    number2 = number; // Duplicates the users input.

    while (number2 != ZERO) // Checks to see if the user entered a '0'.
    {

        //Extraction process
        n1 = number % 10;
        number /= 10;
        n2 = number % 10;
        number /= 10;
        n3 = number % 10;
        number /= 10;


        cout << "The digits in the number " << number2 << " are " << n3 << ", " << n2 << ", and " << n1 << "." << endl;

        cout << "Please enter a value between 1 and 999. Your may enter '0' to exit." << endl;

        number = readInt("The Number", 0, 999);

        number2 = number;
    }
    cout << "Thanks for using this program!" << endl;

    system("pause");
    return 0;
}
/*
*************************************readInt***********************************
description: Reads and validates an integer in the range between min and max.
        errorMsg: Describes to user the type of data to reenter if error encountered
        min:    The minimum acceptable value.
        max:    The maximum acceptable value.
precondition: User has been prompted for input
    errorMsg may be assigned a value, default argument is empty string
    min and max may be assigned values, default arguments are system defaults for int
    uses header files:  iostream, sting, limits, cctype.
postcondition: A valid integer in the range min to max is returned.
*/
int readInt(string errorMsg, int min, int max)
{
    int someInt;            // Stores each integer entered
    bool valid = false; // Loop control flag indicating validity of entry
    // initially assuming not valid.
    do
    {
        // Read an integer delimited by a whitespace character
        cin >> someInt;

        // Valid if within min to max range.
        valid = someInt >= min && someInt <= 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 someInt; // Returns a valid integer to calling environment.
}