How would I filter out non-int entries?

This is a discussion on How would I filter out non-int entries? within the C++ Programming forums, part of the General Programming Boards category; I am making a menu for a console program (a homework assignment). The menu is set up so that the ...

  1. #1
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    How would I filter out non-int entries?

    I am making a menu for a console program (a homework assignment). The menu is set up so that the use may enter an int 1-9 but when they enter an int outside the 1-9 range they get an "Invalid Entry" messege.


    Currently, if I try to enter a non-int character or a string the program crashes. My question is how do I make it so the program filters out non-int entries?


    Here is my code...

    Code:
    #include <iostream>
    using namespace std;
    
    
    int main(){
    
        int selection;
        
        cout << "Please select from the following:\n\n"
             << "1.  Add Customer\n"
             << "2.  Delete Customer\n"
             << "3.  Change Customer Name\n"
             << "4.  Rent Video\n"
             << "5.  Return Video\n"
             << "6.  Renew Video\n"
             << "7.  Report Overdue Videos\n"
             << "8.  Report Checked Out Videos\n"
             << "9.  Search for Customer\n\n";
        
        cin >> selection;
        cin.get();
        
        if( selection < 1 || selection > 9 )
            cout << "Invalid Entry";
        
        else
            cout << "Valid Entry";
            
        return 0;
    }

  2. #2
    Registered User MacNilly's Avatar
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    After you cin >> something, you must check for the inputstream to be in a fail condition using cin.fail(). If it is in a fail state, you cin.clear() it and also ignore the data in the input stream (buffer?) using the cin.ignore() function.

    Code:
    do
    {
         cout << prompt;
         cin >> input;
         
         if (cin.fail())
         {
                  cin.clear();
                  cin.ignore(numeric_limits<streamsize>::max(), '\n');
         }
         else if (input < low || input > high)
                  cout << errMsg << endl;
    }
    while (!cin.fail() && (input < low || input > high));
    
    return input;
    This is a small section of code from a C++ InputValidation class that I had made for my OO C++ class assingments which comes in very handy in all sorts of programs.

  3. #3
    The superhaterodyne twomers's Avatar
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    Ireland
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    Code:
        cout << "Please select from the following:\n\n"
             << "1.  Add Customer\n"
             << "2.  Delete Customer\n"
             << "3.  Change Customer Name\n"
             << "4.  Rent Video\n"
             << "5.  Return Video\n"
             << "6.  Renew Video\n"
             << "7.  Report Overdue Videos\n"
             << "8.  Report Checked Out Videos\n"
             << "9.  Search for Customer\n";
    
        while ( cout << "\nEnter your selection: " && !(cin >> selection)
                && selection>=1 && selection <=9 )
        {
            cout<< "Bad selection!";
    
            cin.clear();
            cin.ignore(std::numeric_limits < int >::max(), '\n');
        }
    is another option from the FAQ

  4. #4
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    If the options are '1' through '9' only, another possibility is to read in the input as a character and check it to make sure it is between '1' and '9' (note the single quotes which are necessary to indicate characters instead of numbers). This has the advantage of avoiding the checking of cin for fail state (all characters are valid) and using ignore() and clear().

  5. #5
    Registered User
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    Thanks for your input guys, it's just what I needed.

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