Verifying User Input as a Double

[joatmon]

Is there a simple way to verify that a user input is consistent with type double?

like:
double n;
cout << "Please enter a number between 0 and 1: ";
cin >> n;

But, if the user inputs "x" or something non-conforming, my program blows up. I tried getline, but that is messy.

Is there an easy answer to this?

Thanks.

[hamsterman]

If >> fails (due to a string being where a number should be, for example), fail flag is set. Note that this flag can be checked with cin.fail() or simply evaluating cin to a boolean. To proceed with any other input, you need to clear that flag.
Your code could be

double n;
cout << "Please enter a number between 0 and 1: ";
while( !( cin >> n ) ){//this will be true if an error occurs. It could be while( cin.fail() )
                       //but then you'd have to add the actual input
   string str;
   cin.clear();//you need to clear the flags before input
   getline( cin, str );//read what was written. Since you probably don't need this, look into cin.ignore()
   cout << str << " is not a number\n";
}

[ResidentBiscuit]

I've got a similar problem. I have a program that has an array in it that is user inputted. The array is of int data type, and I need a way to validate that the data entered is an int for every iteration of the loop. Here's my loop. Just a basic for loop.

    //get input
    for(int x = 0; x < 10; x++)
    {
        cin >> pancakes[x];
    }

In my program, if you enter a char or string into this, it just cuts out of the loop and outputs a bunch of huge ints. So I would like a way to check every loop if the data is an int, and if not allow the user to re enter the data for that part of the array. I've tried a couple things, none of them worked. :(

[joatmon]

Thanks, but I have a question about this. How would >> fail? Let's say that a user entered "x" instead of a number. cin >> wouldn't fail, per se, it would accept the input and move along. It's me that would still have the same problem in that I have to go through all sorts of verifications to check whether this input is conforming or not.

Am I not understanding this? Thanks.

[hamsterman]

In this case, "to fail" means "to set a fail flag".

[joatmon]

Got it. Thanks!