using isdigit()

This is a discussion on using isdigit() within the C Programming forums, part of the General Programming Boards category; hi! i'm trying to check if a string has numbers or chars, for example: char string[3]; how can i accomplish ...

  1. #1
    Registered User IndioDoido's Avatar
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    using isdigit()

    hi!

    i'm trying to check if a string has numbers or chars, for example: char string[3];

    how can i accomplish this using isdigit() or with other method?
    "Artificial Intelligence usually beats natural stupidity."

  2. #2
    and the hat of wrongness Salem's Avatar
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    isdigit() and a loop.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  3. #3
    and the hat of sweating
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    Use a loop and check each character with isdigit().
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

    "the internet is a scary place to be thats why i dont use it much." - billet, 03/17/2010

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    isdigit() checks for digits and isalpha() checks for letters.

  5. #5
    Registered User IndioDoido's Avatar
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    Code:
    char ipend[3];
    
    size = strlen(ipend);
    
    for(i=0; i<=size; i++)
    {
    	if( isdigit(ipend[i]) )
    	{
    		MessageBox(hWnd, "digit", "digit", MB_OK);
    	}
    	else MessageBox(hWnd, "non digit", "non digit", MB_OK);
    }
    i tried this but it doesn't work properly
    it works fine with the 2 first characters of the string, but it doesn't seem to check the last one correctly.
    "Artificial Intelligence usually beats natural stupidity."

  6. #6
    and the Hat of Guessing tabstop's Avatar
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    By the last character, do you mean the \0 terminating character? Is there supposed to be something in ipend already?

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    That's because strlen() does not count the terminating null byte if its already populated. Use the sizeof operator instead.

  8. #8
    and the hat of wrongness Salem's Avatar
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    > it works fine with the 2 first characters of the string, but it doesn't seem to check the last one correctly.
    char [3] can only hold 2 characters, and a \0.

    Otherwise, you're trashing memory.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  9. #9
    Registered User IndioDoido's Avatar
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    i tried: size = sizeof(ipend);

    but the it doesn't work neither
    "Artificial Intelligence usually beats natural stupidity."

  10. #10
    and the hat of wrongness Salem's Avatar
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    Back to basics, how did you populate your string?
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  11. #11
    and the hat of sweating
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    With the code as it's shown, the string contains whatever garbage was in memory.
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

    "the internet is a scary place to be thats why i dont use it much." - billet, 03/17/2010

  12. #12
    Registered User IndioDoido's Avatar
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    Code:
    char ipend[3];
    		
    size = sizeof(ipend);
    
    for(i=0; i<=size; i++)
    {
    	if( isdigit(ipend[i]) )
    	{
    		MessageBox(hWnd, "digit", "digit", MB_OK);
    	}
    	else MessageBox(hWnd, "non digit", "non digit", MB_OK);
    }
    "Artificial Intelligence usually beats natural stupidity."

  13. #13
    Woof, woof! zacs7's Avatar
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    Wrong again. ipend[3] is out of bounds.

    Stop "hacking" at it, learn and do it properly.

  14. #14
    and the hat of sweating
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    And ipend still contains garbage.
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

    "the internet is a scary place to be thats why i dont use it much." - billet, 03/17/2010

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