r3dux.org

#include <iostream>
using namespace std;
 
int main()
{
    int yearsOld       = 0;
    bool gotValidInput = false;
 
    do
    {
        cout << "Please enter your age in years: ";
        cin >> yearsOld;
 
        if (cin.fail())
        {
            cin.clear();
            cin.ignore();
            cout << "Invalid entry! Whole numbers only, dawg!" << endl;
        }
        else
        {
            // We got some valid input! Set the flag so we can leave the loop!
            gotValidInput = true;
        }
 
    } while ( gotValidInput == false );
 
    cout << "Valid value is: " << yearsOld << endl;
 
    return 0;
}

#include <iostream>
#include <sstream>
 
using namespace std;
 
int getValidInteger(string prompt)
{
    bool debug = true;                        // Toggle for verbosity
 
    bool   valid;                             // Our exit flag - we only get out of the do..while loop when this is true
    bool   mixedOperators;                    // Did the user enter a mixture of + and - operators (i.e. -5+3)
    bool   multipleOperators;                 // Did the user enter multiple + or - operators      (i.e. -5-3 or +5+3)
    int    userInt = 0;                       // Integer value we finally return after validation
    string userInput;                         // User input is taken as a string before being wrangled...
    int    foundInvalidInputLocation;         // Character location of any invalid input
 
    string validCharacters  = "+-0123456789"; // All the valid characters we're willing to accept as valid integer input
 
    do
    {
        // Set our initial flags
        valid                     = false;
        mixedOperators            = false;
        multipleOperators         = false;
        foundInvalidInputLocation = 0;
 
        // Display the prompt and get the user input as a string
        cout << endl << prompt << endl;
        getline(cin, userInput);
 
        // Convert the user input string into a input stringstream then...
        istringstream iss(userInput);
 
        // ...try to convert the istringstream into an integer.
        if (iss >> userInt)
        {
            if (debug)
            {
                cout << "This already is or can be made into a valid integer!" << endl;
            }
 
            // Now cast our input string-stream back to a string and...
            string test = iss.str();
 
            // ...test to see if we found any illegal characters (because "123Foo!" -WILL- convert to the int 123, but we want legit input!
            foundInvalidInputLocation = test.find_first_not_of(validCharacters);
 
            if (debug)
            {
                cout << "Value of foundInvalidInputLocation is: " << foundInvalidInputLocation << endl;
            }
 
            // Check whether we found an character which cannot be part of a valid int (-1 indicates no invalid character found)
            if (foundInvalidInputLocation != -1)
            {
                if (debug)
                {
                    cout << "Although we can cast the provided input to an int..." << endl;
                    cout << "...the original input contained at least one invalid character at location: " << foundInvalidInputLocation << endl;
                }
            }
            else // No non-digit characters found? Then we were likely given a legitimate int - but we still need to do more testing to be sure!
            {
                // Find the locations of the first and last plus and minus operators in our converted-from-iss string
                int firstMinusOperatorLoc = test.find_first_of("-");
                int lastMinusOperatorLoc  = test.find_last_of("-");
                int firstPlusOperatorLoc  = test.find_first_of("+");
                int lastPlusOperatorLoc   = test.find_last_of("+");
 
                if (debug)
                {
                    // Wax lyrical about multiple negative operators if detected...
                    cout << "First and last minus signs are at: " << firstMinusOperatorLoc << " and " << lastMinusOperatorLoc << " Match?: ";
                    firstMinusOperatorLoc == lastMinusOperatorLoc? cout << "Yes! This is good!" << endl : cout << "No! Multiple minus operators detected!" << endl;
 
                    // Wax lyrical about multiple positive operators if detected...
                    cout << "First and last plus signs are at: " << firstPlusOperatorLoc << " and " << lastPlusOperatorLoc << " Match?: ";
                    firstPlusOperatorLoc == lastPlusOperatorLoc? cout << "Yes! This is good!" << endl : cout << "No! Multiple plus operators detected!" << endl;
                }
 
                // Got a mixture of both positive and negative operators in the input? Then it's not a valid int!
                if ( (firstMinusOperatorLoc != -1) && (firstPlusOperatorLoc != -1) )
                {
                    if (debug)
                    {
                        cout << "Mixed + and - operators detected, so flagging this as invalid input!" << endl;
                    }
 
                    mixedOperators = true;
                }
                else // No mixed operators? Then we can continue to check for multiple operators...
                {
                    if (debug)
                    {
                        cout << "No mixed operators - continuing... " << endl;
                    }
 
                    // Got multiple negative or positive operators in the input? Then it's not a valid int!
                    if ( (firstMinusOperatorLoc != lastMinusOperatorLoc) || (firstPlusOperatorLoc != lastPlusOperatorLoc) )
                    {
                        if (debug)
                        {
                            cout << "Multiple + or - operators detected, so flagging this as invalid input!" << endl;
                        }
 
                        multipleOperators = true;
                    }
                    else
                    {
                        if (debug)
                        {
                            cout << "No multiple operators - continuing... " << endl;
                        }
                    }
 
                } // End of if mixed operator check else-block
 
                // If we've finally got here and we don't have mixed or multiple operators - then FINALLY we know we have a valid int...
                if ( (mixedOperators == false) && (multipleOperators == false) )
                {
                    if (debug) { cout << "Got a truly valid int! Hurrah!" << endl; }
 
                    // ...so set our exit flag to get out of the do..while loop
                    valid = true;
                }
 
            } // End of if (foundInvalidInputLocation != -1) else section
 
        } // End of if (iss >> userInt) section
        else
        {
            cout << "That's not a valid integer value!" << endl;
        }
 
    } while (valid == false);
 
    // Because we got out of the loop, we must have a valid integer, which we can now return!
    return userInt;
}
 
 
int main()
{
    int x = getValidInteger("Please enter a valid integer: ");
 
    cout << endl << "The value of our valid integer is: " << x << endl;
 
    //system("pause");
    return 0;
}