Making cin take selective inputs [Turbo C++]

Question

Don't hate cause of Turbo, I already hate my school!

I wish to show an error msg if a character is entered instead of an int or float in some file such as age or percentage. I wrote this function:

template <class Type>
Type modcin(Type var) {
    take_input:  //Label
    int count = 0;
    cin>>var;
    if(!cin){
        cin.clear();
        cin.ignore();
        for ( ; count < 1; count++) { //Printed only once
            cout<<"\n Invalid input! Try again: ";
        }
        goto take_input;
    }
    return var;
}

but the output is not desirable:

How do I stop the error msg from being repeated multiple times? Is there a better method?

NOTE: Please make sure that this is TurboC++ that we are talking about, I tried using the approach in this question, but even after including limits.h, it doesn't work.

This is example of bad use of goto. Don't construct loops with goto. Use actual loops. — hyde, Oct 10 '17 at 13:58
@hyde I understand that, I used goto after I tried for and do-while loops, I was trying different things to eliminate the multiple prints. I posted the goto code cause thats the last try I made. — Ankur Singh, Oct 11 '17 at 03:54
@AnkurSingh you are goto every pass so it is an endless loop... Add `if` so the goto is executed only if you have the wrong input .... but `for` would be nicer with probably much less code ... — Spektre, Oct 11 '17 at 08:06
@Spektre I understand the point but I’ve tried using for and while. It was a while back but I couldn’t get rid of the multiple prints when entering strings into console. I even tried putting cin>>var; out of the loop and checking it’s state in a while loop but that gave me multiple outputs too for some reasons. — Alpha Mineron, Oct 19 '17 at 18:03
@Spektre The goto isn't happening on everypass, its not endless. It's only encountered when the input is incorrect. The goto is within the if statement. I've fixed the indent issue. — Ankur Singh, Oct 21 '17 at 17:30

Alpha Mineron · Accepted Answer · 2017-10-21T20:59:28.650

Here, a code snippet in C++.

template <class Type>
Type modcin(Type var) {
    int i=0;
    do{
        cin>>var;
        int count = 0;
        if(!cin) {
            cin.clear();
            cin.ignore(numeric_limits<streamsize>::max(), '\n');
            for ( ; count < 1; count++) {  //Printed only once
                cout<<"\n Invalid input! Try again: ";
                cin>>var;
            }
        }
    } while (!cin);
    return var;
}

The variables are tailored to match yours' so you can understand better. This code isn't perfect though.

It can't handle cases like "1fff", here you would just get a 1 in return. I tried solving it but then a infinite loop was being encountered, when I'll fix it, I'll update the code.
It also can't function in TurboC++ effectively. I don't know if there are alternatives but the numeric_limits<streamsize>::max() argument gives a compiler error ('undefined symbol' error for numeric_limits & streamsize and 'prototype must be defined' error for max()) in Turbo C++.

So, to make it work in Turbo C++. Replace the numeric_limits<streamsize>::max() argument with some big int value such as 100. This will make it so that the buffer is only ignored/cleared till 100 characters are reached or '\n' (enter button/newline character) is pressed.

EDIT

The following code can be executed on both Turbo C++ or proper C++. The comments are provided to explain the functioning:

template <class Type>             //Data Integrity Maintenance Function
Type modcin(Type var) {           //for data types: int, float, double
    cin >> var;
    if (cin) {  //Extracted an int, but it is unknown if more input exists
         //---- The following code covers cases: 12sfds** -----//
        char c;
        if (cin.get(c)) {  // Or: cin >> c, depending on how you want to handle whitespace.
            cin.putback(c);  //More input exists.
            if (c != '\n') {  // Doesn't work if you use cin >> c above.
                cout << "\nType Error!\t Try Again: ";
                cin.clear();  //Clears the error state of cin stream
                cin.ignore(100, '\n');  //NOTE: Buffer Flushed <|>
                var = modcin(var);  //Recursive Repeatation
            }
        }
    }
    else {    //In case, some unexpected operation occurs [Covers cases: abc**]
        cout << "\nType Error!\t Try Again: ";
        cin.clear();  //Clears the error state of cin stream
        cin.ignore(100, '\n');  //NOTE: Buffer Flushed <|>
        var = modcin(var);
    }
    return var;

//NOTE: The '**' represent any values from ASCII. Decimal, characters, numbers, etc.
}

Making cin take selective inputs [Turbo C++]

1 Answers1

EDIT