Input Checking

#include <iostream>
#include <string>

using namespace std;

void getNoColors(int *no_colors);

int main(void)
{
    int noColors = 0;

    getNoColors(&noColors);

    return 0;
}

void getNoColors(int *no_colors)
{
    bool invalid = true;
    long int cGuard = 0;
    string iGuard = "";

    //Do-While to continuously loop until input is valid
    do
    {
        /* Don't just cin >> *no_colors. If the user enters a non-numeric character,
           your input will never stop looping with an error (your solution would not
           face this particular problem, as it doesn't loop on an input error).

           Last cin.get() is to remove newline from stream
        */
        cout << "Enter the number of colors to display (Between 2 and 5 inclusively): ";
        cin >> iGuard;
        cin.get();

        //Convert string input; safe conversion is to long int.
        //We'll check that it doesn't pass int range after.
        cGuard = atoi(iGuard.c_str());
        *no_colors = (int) cGuard;

        //Remember, C++ does short-circuit checking, so if cGuard is out of range,
        //we'll never even check if *no_colors is in range.
        invalid = cGuard > INT_MAX || cGuard < INT_MIN || *no_colors < 2 || *no_colors > 5;

        if(invalid)
            cout << "ERROR: Invalid input.\n\n";

    }while(invalid);
}