cctype functions

This is a discussion on cctype functions within the C++ Programming forums, part of the General Programming Boards category; I'm rather new at C/C++ and I'm having trouble understanding how these things work. I'm reading a tutorial on them ...

  1. #1
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    cctype functions

    I'm rather new at C/C++ and I'm having trouble understanding how these things work. I'm reading a tutorial on them but I don't understand the return values that I'm getting. Let's use the isdigit() function as an example, the tutorial says:
    The isdigit() function returns non-zero for true and zero for false. If the parameter is not in the domain of the function, the return result is undefined.
    Now suppose that I use the following code:
    Code:
     int var_one = 1;
     bool var_two = isdigit(var_one);
     cout << var_two << endl;
    The program will output a 0 for false, but var_one is a digit. What am I missing here?

  2. #2
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    isdigit(1);
    Is false

    isdigit('1');
    is true

    It's for testing characters which you might type in at the keyboard, or read from a text file.

    Eg, if you ask the user to enter a number, and they enter "abc", you can use isdigit() to verify the data entry.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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    Thanks, I see where I was going wrong now -- expected the 1 to be evaluated as an an integer and not as a character :P

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