Character handling help

This is a discussion on Character handling help within the C Programming forums, part of the General Programming Boards category; I've been workin on the following program and could use a little help. The program should input a character from ...

  1. #1
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    Character handling help

    I've been workin on the following program and could use a little help. The program should input a character from the keyboard and using isdigit, return wheter the character is a digit or not. The program compiles fine, but will not function. I get a program error and the window is closed. I also tried to input the character into the isdigit function as a pointer to character and that also would not work.

    Code:
    #include <stdio.h>
    #include <ctype.h>
    
    int main()
    {
       int character;  /* Initializes character  */
     
       printf( "Enter a character: ");    /* Asks for character and inputs it */     
       scanf( "%d", character );
    
               /* This should determine if the character is a digit or not */
       printf( "%d%s", isdigit( character ) ?  "The character is a " : "The character is not a ", "digit." );   
    
       return 0;
    }
    Thanks!

  2. #2
    C++ Developer XSquared's Avatar
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    You're missing the number. According to the first argument you're passing to printf, it expects a number and a string. You're just passing a string.
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  3. #3
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    Code:
    printf( "%d%s", isdigit( character ) ?  "The character is a " : "The character is not a ", "digit." );
    Here printf() expects an integer and a string. You are passing two strings. If character is a digit, then the first string is "The character is a", else the first string is "The character is not a". the second string is "digit.".

    Also you expect a character, so variable character could be of type char and you should read a character.

    Code:
       char character;
    
       scanf( "%c", &character);

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    Thanks for the help.
    Last edited by vandalay; 11-23-2003 at 01:06 AM.

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    Any ideas on how I can get the program to take whitespace characters and test them as well? I'm able to enter and check single characters, but it needs to check short strings also.

  6. #6
    and the hat of wrongness Salem's Avatar
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    Generally speaking, you should always use fgets() to read the input into a buffer.

    Then you have all the freedom to use as many buffer oriented functions (including sscanf()) to extract information from that buffer.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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    Originally posted by Salem
    Generally speaking, you should always use fgets() to read the input into a buffer.

    Then you have all the freedom to use as many buffer oriented functions (including sscanf()) to extract information from that buffer.
    I havent quite worked my way up to that yet. Any suggestions using arrays or pointers?

  8. #8
    Been here, done that.
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    Originally posted by vandalay
    I havent quite worked my way up to that yet. Any suggestions using arrays or pointers?
    scanf() is so full of problems when dealing with mixed input (numbers, strings, whitespace) that you will spend a LOT of time trying to figure it out, then when you learn how to use fgets() you will see a much better way to handle input. YOU have the control instead of cobbling together unreadable format specifiers. If you must, learn scanf() fully. But I'd recommend either waiting for fgets() and learn how to parse a string then, or look into fgets() now... Beat the rush.
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  9. #9
    ... kermit's Avatar
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    Originally posted by vandalay
    Any ideas on how I can get the program to take whitespace characters and test them as well? I'm able to enter and check single characters, but it needs to check short strings also.
    I am assuming that because you know of isdigit() you also are aware of isspace()?

    ~/

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    Originally posted by kermit
    I am assuming that because you know of isdigit() you also are aware of isspace()?

    ~/
    Thats the part of the program I'm having trouble with. I'm unable to enter a string such as \n or \t to test to see if its a whitespace character. I'm only able to enter a single character. When \n is entered, only \ is tested.

  11. #11
    ... kermit's Avatar
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    Is there a reason why you could not use the getchar() function? It works nicely for such things.

    Code:
    #include <stdio.h>
    #include <ctype.h>
    
    int main( void )
    {
       int *character;  /* Initializes character  */
     
       printf( "Enter a character: ");    /* Asks for character and inputs it */     
       *character = getchar();
    
               /* This should determine if the character is a digit or not */
       printf( "\n%s%s", isdigit( *character ) ?  "The character is a " : "The character is not a ", "digit.\n\n" );   
    
       return 0;
    }
    [edit]
    Sorry, I should have paid better attention - the digit thing was solved, you need to know about spaces now. You can do that with getchar too, but using fgets() might be your bets bet, as was previously mentioned, as the stuff is already nicely in a buffer for you, and you can do any test on the contents of the buffer you desire.
    ~/
    Last edited by kermit; 11-23-2003 at 03:31 PM.

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    Originally posted by kermit
    Is there a reason why you could not use the getchar() function? It works nicely for such things.

    Code:
    #include <stdio.h>
    #include <ctype.h>
    
    int main( void )
    {
       int *character;  /* Initializes character  */
     
       printf( "Enter a character: ");    /* Asks for character and inputs it */     
       *character = getchar();
    
               /* This should determine if the character is a digit or not */
       printf( "\n%s%s", isdigit( *character ) ?  "The character is a " : "The character is not a ", "digit.\n\n" );   
    
       return 0;
    }
    [edit]
    Sorry, I should have paid better attention - the digit thing was solved, you need to know about spaces now. You can do that with getchar too, but using fgets() might be your bets bet, as was previously mentioned, as the stuff is already nicely in a buffer for you, and you can do any test on the contents of the buffer you desire.
    ~/
    Thanks Kermit. I tried your suggestion and still only get the \ of \n or \t to test against isspace. Any other recommendations?

  13. #13
    ... kermit's Avatar
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    Could you possibly give a little context as to what you want to do with this input, and why you are testing for a space? It might be helpful in order to figure out which direction to take, as there are many ways of doing things in C a lot of the time it seems.

  14. #14
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    Sorry about that. I have to input a character from the keyboard and test it against the functions in the character handling library. I have all of the functions working, except the ones requiring a string (\n, \t, \r, and such). In those, the only thing recognized is \. I've tried everything I can think of, which isnt a whole lot. Thanks for your patience and help.

  15. #15
    ATH0 quzah's Avatar
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    Code:
    int main( void )
    {
       int *character;  /* Initializes character  */
     
       printf( "Enter a character: ");    /* Asks for character and inputs it */     
       *character = getchar();
    This is entirely wrong. You should not be using a pointer here. getchar returns a character, not a pointer to a character. Furthermore, since you are using a pointer, and you aren't actually making it point to something, it points to some random space in memory.

    What happens is that as soon as you call getchar the way you are, it overwrites that random spot in memory with whatever getchar returns. This is a BadThing(TM).

    Don't use a pointer. Nothing here requires a pointer.

    Quzah.
    Hope is the first step on the road to disappointment.

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