Data validation

This is a discussion on Data validation within the C Programming forums, part of the General Programming Boards category; Hi, I want to check that user input is a letter only. I have managed to trap it for lower ...

  1. #1
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    Data validation

    Hi,

    I want to check that user input is a letter only. I have managed to trap it for lower case vs upper case using this code:

    Code:
    if ("%d" > 64 || "%d" < 91, letter, letter)
      {
      letter = letter+32;
      }
    I also want to prompt the user to enter a correct letter in case they choose a number or a symbol. Can this be done the same way by manipulating the ascii table? I have no issue doing that except for the characters between the lower case and uppercase letters....is there a way to isolate those characters using logical operators? I hope I make sense!!

    Thanks

  2. #2
    CSharpener vart's Avatar
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    I have managed
    Do you mean this code works for you?
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  3. #3
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    Quote Originally Posted by vart View Post
    Do you mean this code works for you?
    Doh!!! Nope doesn't work! It now accepts the upper case letters, but not the lower case letters!!!

    Are you able to point me in the right direction as to what I should be looking for?

    Thanks

  4. #4
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    the c library already has functions that do this. in ctype.h the tolower function will return the lower case equivalent or the same character if there isn't a lower case equivalent. the toupper function does the opposite of tolower. if you just want to check the case, isupper and islower will do that, and if you want to check for a letter, isalpha does that.

  5. #5
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    Excellent...thanks for that....Will check now

  6. #6
    C++まいる!Cをこわせ! Elysia's Avatar
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    The "%x" stuff doesn't work for if statements!
    Please consult your books again.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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