Sample C code that change character

This is a discussion on Sample C code that change character within the C Programming forums, part of the General Programming Boards category; Hi all, First of all, i have to make it clear that i am not asking anyone to do my ...

  1. #1
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    Sample C code that change character

    Hi all,
    First of all, i have to make it clear that i am not asking anyone to do my homework.

    All i want is, do anyone have sample C code that change all the lower case chacter to upper case and vis versa.
    For example, a file that will contain all the characters, space and punctation, the C code will take in the file and change all the upper case to lower and lower case to upper case instead of using the toupper() and to lower().

    input => This is an Example.
    output => tHIS IS AN eXAMPLE.
    diana --> programming is tough

  2. #2
    FOX
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    Use the functions isupper(), islower(), toupper() and tolower() from ctype.h.


    Code:
    #include <ctype.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    
    static char *strtolower(const char *src)
    {
            char *dest = malloc(sizeof(char) * (strlen(src)+1));
    
            int i = 0;
            while (src[i])
            {
                    dest[i] = isupper(src[i]) ? tolower(src[i]) : toupper(src[i]);
                    ++i;
            }
            dest[i] = '\0';
            return dest;
    }
    
    int main(void)
    {
            char *p = strtolower("Hello, World!");
            printf("%s\n", p);
            return 0;
    }
    Last edited by ^xor; 05-29-2005 at 03:48 AM. Reason: Improved code

  3. #3
    and the hat of wrongness Salem's Avatar
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    Wouldn't it have been clearer to just use dest[i] = src[i] etc, rather than introduce another variable and another style into the function?
    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.

  4. #4
    Gawking at stupidity
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    Or just really simply:
    Code:
    itsme@itsme:~/C$ cat switchcase.c
    #include <stdio.h>
    #include <ctype.h>
    
    int main(void)
    {
      int c;
    
      while((c = getchar()) != EOF)
        putchar(isupper(c) ? tolower(c) : toupper(c));
    
      return 0;
    }
    Code:
    itsme@itsme:~/C$ cat file.txt
    ThiS Is teXt wITH
    rANDom CAPItaliZatiOn
    itsme@itsme:~/C$ ./switchcase < file.txt
    tHIs iS TExT With
    RandOM capiTALIzATIoN
    itsme@itsme:~/C$
    If you understand what you're doing, you're not learning anything.

  5. #5
    FOX
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    I wasn't sure if toupper/tolower would try to convert non-alpha characters, but looking at your solution it appears they don't.

  6. #6
    Yes, my avatar is stolen anonytmouse's Avatar
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    Code:
    #include <stdio.h>
    #include <ctype.h>
    
    int main(void)
    {
      int c;
    
      while((c = getchar()) != EOF)
        putchar(isupper( (unsigned char) c) ? tolower( (unsigned char) c) : toupper( (unsigned char) c));
    
      return 0;
    }

  7. #7
    Gawking at stupidity
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    I don't know about your compiler, but the prototypes for those ctype.h functions on my system are:

    int isupper(int c);
    int toupper(int c);
    int tolower(int c);

    So what's with the typecasting?

    [edit]
    I just stumbled across this in the man page for the ctype.h functions:
    If c is not an unsigned char value, or EOF, the behaviour
    of these functions is undefined.
    So I guess that's why you added the typecasting. However, the getchar() man page mentions:
    [getchar()] reads the next character from stream and returns
    it as an unsigned char cast to an int, or EOF
    on end of
    file or error.
    So since I'm not changing the value between the getchar() and the tolower()/toupper() calls, it's safe without the typecasting anyway.
    [/edit]
    Last edited by itsme86; 05-29-2005 at 03:17 AM.
    If you understand what you're doing, you're not learning anything.

  8. #8
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    Ya i have tried and both give the same out put...

    But both uses the function "toupper()" and "tolower()", is there any examples that does not use this two given functions and still produce the same result...

    Can anyone tell me what does "? and :" in the "while" loop means.

    Thanks....
    diana --> programming is tough

  9. #9
    Yes, my avatar is stolen anonytmouse's Avatar
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    >> So since I'm not changing the value between the getchar() and the tolower()/toupper() calls, it's safe without the typecasting anyway. <<

    Yep, I wasn't aware of that requirement of getchar (I should have checked). As a pattern, I think it is a good idea to always use the cast with these functions. At least that's my pathetic excuse...

    >> Can anyone tell me what does "? and :" in the "while" loop means. <<

    This is called the conditional expression operator. It it a shortcut version of if/else. You can find more info with this search.

  10. #10
    and the Hat of Clumsiness GanglyLamb's Avatar
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    Quote Originally Posted by dianazheng
    is there any examples that does not use this two given functions and still produce the same result...
    you can check this http://web.cs.mun.ca/~michael/c/ascii-table.html

    Basically what you will notice is that to convert a character from uppercase to lowercase you will have to add 32 (decimal) to the decimal value of the upper case letter.

    To go from lower case to uppercase just subtract 32 (decimal) to get the decimal representation of the uppercase letter.

    Just involves some if structures to make sure you are not dealing with non-letter characters.

    This way you dont need any function like toupper or tolower - actually it makes me remember these stupid exercises during my assembler class

  11. #11
    and the hat of wrongness Salem's Avatar
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    > is there any examples that does not use this two given functions
    And when your character set isn't ASCII, you'll be glad you used tolower() etc rather than some hack involving adding or subtracting 32.
    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.

  12. #12
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    Ya, i know that its better to use the functions available.

    But i just want to know that how can we do that without using the available function.

    Also how the code will look like and exposed myself to that.
    diana --> programming is tough

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