How to handle spaces in strings

This is a discussion on How to handle spaces in strings within the C Programming forums, part of the General Programming Boards category; Hi everyone, I'm writing code that uses an encoding called rot13, where each letter is shifted 13 spaces, so "a" ...

  1. #1
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    How to handle spaces in strings

    Hi everyone,

    I'm writing code that uses an encoding called rot13, where each letter is shifted 13 spaces, so "a" becomes "n" and "b" becomes "o" etc. It was an old C assignment.

    The problem:

    When I enter Hello world, only hello is converted and not world.

    Any ideas?

    Code:
    /*
    Description: ROT13 encoding; to change each letter of a word 13 places along the alphabet. i.e, a
    becomes n.
    Input is from keyboard
    modified date:26/11/04
    */
    
    #include <stdio.h>
    //#include <CLIB.H>     Commented out because it produces errors
    #include <string.h>
    main(){
       char rot13[100];
       int i=0;
           
       printf("Enter word  n ");
       scanf("%s",rot13);
    
       for(i=0;i<(strlen(rot13));i++)
       {
                                     
           if (('a'<=rot13[i])&&(rot13[i]<='n'))
           {
                   rot13[i]= rot13[i] + 13;
           }
           else if (('m'<=rot13[i])&&(rot13[i]<='z'))
           {
                           rot13[i]= rot13[i] - 13;
           }
           else if (('A'<=rot13[i])&&(rot13[i]<='N'))
           {
                           rot13[i]= rot13[i] + 13;
           }
           else if (('N'<=rot13[i])&&(rot13[i]<='Z'))
           {
                           rot13[i]= rot13[i] - 13;
           }                   
           else if (rot13[i]== 32)                                 // 32 is ACSII for space
           {
                            rot13[i] = ' ';
                         
           } 
        }
    
       printf("%s\n",rot13);
       system("PAUSE");                                            // There is a better away to stop the program from quiting, not sure what it is
     }

  2. #2
    Epy
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    Maybe try fgets instead of scanf.

  3. #3
    Registered User hk_mp5kpdw's Avatar
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    Quote Originally Posted by Epy View Post
    Maybe try fgets instead of scanf.
    Or...
    Code:
       char rot13[100];
       int i=0;
           
       printf("Enter word  n ");
       scanf("%99[^\n]",rot13);
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
    -Christopher Hitchens

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    Thanks Epy.

    I haven't been able to find a good example of fgets and as far as I can see it only referes to reading data from files. Can you point me to a good example of fgets?

    I'll keep looking into it. Thanks.

  5. #5
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    Brilliant hk_mp5kpdw, that worked.

    I'm not sure what, 99[^\n] does though.

    "%s", must only accept a string untill a space is pressed, so 99[^\n] must accept 99 charaters?

    edit: %s is a type of Format Specifier for scanf:

    C - printf and scanf, Format Specifiers
    Last edited by a_satari; 04-05-2010 at 07:48 AM.

  6. #6
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    %[ABCD........XYZ] causes only the characters inside the brackets to be read by scanf ; if any other character is found then it terminates.

    Oppositely in case of %[^\n]
    the circumflex(^) causes every character to be read except the character inside the brackets, which becomes the terminating character.here \n is the terminating character.

    So its a useful way for scanf sometimes.

  7. #7
    spurious conceit MK27's Avatar
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    Quote Originally Posted by a_satari View Post
    I'm not sure what, 99[^\n] does though.
    C - printf and scanf, Format Specifiers
    Because that documentation is unfortunately half-assed, and fails to mention a number of format specifiers such as the rather important []. Eg, to capture an alphanumeric string (no spaces, no punctuation):
    Code:
    scanf("%[a-zA-Z0-9]", string_ptr);
    An example of fgets for user input:
    Code:
    char input[256];
    fgets(input,256,stdin);
    fgets() is very useful in combination with sscanf() -- notice, two ss -- since you can simply get all the input into a string, extract what you want from the string, and the then discard the rest, rather than messing around using scanf() on input directly.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

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