Determining if input is int, double, or char

Alright, I'm writing a program that calculates a grade average. I want to allow users to input integers (80, for instance), doubles (92.5), or letters (A, F, a, f, etc).

Basically, I'll be adding whatever the user enters to a total (letter grades will be given a predefined value... A will be 100, for instance, unless I can also allow for A+ type grades, but I'm not worried about that), and then dividing it by the total number of grades entered.

Main will prompt the user to input a grade, using the following as examples (85, 92.3, D), and then store their answer in the appropriate variable. What I don't know is how to determine if what they entered is an integer, a double, or a letter (I don't want to make a long if statement like "if (input == a) || (input == A) || (input == b) ||" and so on. I think I have a good way to determine if the input is a whole number or double (using modulus), so really I just want to know if there's a simple way to determine if input is a letter or number and then determine which variable to store it in.

I figure I'll have to use an overloaded extraction operator, but that still doesn't help me with the letter issue.

If I -have- to go with the long if (grade == A)... statement, then I will, but I want to know if there's a simpler way.

This is homework and not for practical use.

Thanks for any and all help.

You can check the return value of cin >> after attempting to read into a double. If it is false, then the read failed and it was not a number, then use clear() to clear the fail state of cin and read it into a string (or a char if you won't allow B-, B+, etc). You can't read it into a string or char first because even numbers will be read into a string correctly as digit characters.

I don't think you should distinguish between whole numbers and floating-point numbers (doubles). If you have some reason to, then you might have to read the whole thing into a string and search for the '.' character. But again, that shouldn't be necessary.

You could read in the user's input with fgets() and use isdigit() etc (<ctype.h>) to parse it.

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Whoops, this is the C++ board.
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Originally Posted by Daved

You can check the return value of cin >> after attempting to read into a double. If it is false, then the read failed and it was not a number, then use clear() to clear the fail state of cin and read it into a string (or a char if you won't allow B-, B+, etc). You can't read it into a string or char first because even numbers will be read into a string correctly as digit characters.

I don't think you should distinguish between whole numbers and floating-point numbers (doubles). If you have some reason to, then you might have to read the whole thing into a string and search for the '.' character. But again, that shouldn't be necessary.

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Unfortunetely we haven't learned about clear() in class yet, and so it probably won't be allowed in our homework (as she has stated something to this effect before). I half expected most, if not all solutions presented to be unacceptable for homework, but I still have hope.

As far as distinguishing between whole and floating-point numbers go, I am doing it as an example, as this program is going to use polymorphism (I can't believe I left that out). I know it's not practical, but neither is most of the homework we do :P

Thank you for your help, though. Even if I can't use things for my homework, it still expands my knowledge and ability for practical use.

Then I would just read into a string (with cin, not fgets) and parse the string. If the first character is a digit, then you have a number. If the first character is a letter, then you have a grade. If you need to separate whole numbers from floating point, this methods helps with that because you will be checking each digit and can check for '.'.