Easy way to test if input is the correct variable type?

[hrstar24]

So I am using the cin command to have the user get a number value and place it into an int type variable. The problem is that if the user enters an 'a' for example, the program crashes.

Is there a simple loop I can use that checks the variable type, and just outputs "Invalid entry" if a char is entered and asks for another entry?

[gmenfan83]

You would have to validate the input. This should work as long as you are not keeping a tally and have to clear the buffer (something I am still confused and having issues with).

while(!(cin >> your int)
{
     //prompt the user for correct input and loop back
}

Also note that this takes care of your cin input stream all together. If you have

cin >> your int
while(!(cin >> your int)

you will be prompting the user twice, just use

cout << //whatever you say to the user
while(!(cin >> your int)

[Lowest0ne]

I aught to copy/paste this code into notepad or something:

int i;
while (!(cin >> i)){  // If the extraction breaks the cin object
 cin.clear();             // Fix it
 cin.ignore(80, '\n)  // Ignore everything else in the buffer (we hope)

 cout << "You messed up, try again";

}


cin.ignore(80, '\n);  // For if the first entry was valid 

[gmenfan83]

@LowestOne, would the cin.clear(); function clear the buffer if a tally is being kept and restart the tally?

[long double main]

You could also read the input into a string, and use a stringstream to try to convert it to an int.

It would be something like

int yourInt; // This is what you want the user to input
string input;
getline(cin, input);
istringstream convert;
while (convert.str(in), !(convert >> yourInt))
{
    cout << "Bad input, try again: ";
    getline(cin, input);
    convert.clear(); // Clear the error flag
}

[Lowest0ne]

@Long Double Main: wouldn't this ask for two integers the first time around?

Clearing cin would not clear the buffer. I'm not sure if an extraction that breaks cin actually extracts either. I think without the ignore you will still loop forever.

[long double main]

@LowestOne:
I don't think so.
Try it for yourself!

[LB]

clear() clears the error flag. However, the data that caused the error has not been read, and so you will infinitely get errors. You need to sync() after you clear().