Thread: Alphabetical sorting in a character array?

Hi, I'm working on a little program, both for school and just to get better with C, which is supposed to do the following:

• Accept a string input by a user
• Store the string in a character array
• Print out user's string
• Reverse the order of words in user's string (this is an example string = string example an is this)
• Print out the new string
• Sort the letters in each word in alphabetical order (example = aeelmpx)
• Print out the new string

I've done most of my coding using C++ and C# so on top of dealing with the slightly different syntax of C, I've run into a problem on the final two steps, the alphabetical sorting.

So far, this is the code I have:

Code:

// Function to reverse the entire string
void reverseString(char *start, char *end)
{
    // Initialize temporary variable
    char temp;

    while (start < end)
    {
        temp = *start;
        *start++ = *end;
        *end-- = temp;
    }
}

void main (void)
{
    // Initialize variables
    char string[30];
    char *end, *x, *y;

    while (1)
    {
        printf("Enter a string: ");
        gets(string, 30);
        printf("Your string: %s", string);

        // Find end of the string
        for(end = string; *end; end++);

        // Reverse the entire string
        reverseString(string, end-1);

        // Create new start and end points
        x = string-1;
        y = string;

        // Until the end of the string is reached
        while(x++ < end)
        {
            // Reverse each word
            if(*x == '\0' || *x == ' ')
            {
                reverseString(y, x-1);
                y = x+1;
            }
        }

        printf("\nYour reversed string: %s\n\n", string);
    }
}

To clarify some things beforehand, I'll explain some things that I think might be questioned. First, I use void main() instead of int main() because we're supposed to have the program run indefinitely until it's manually shut down so I do not want to return 0 to shut off the program as I would normally. Second, I know scanf() is better than gets() (or at least, I think it is if my research was right) but we're also required to meet a specific size for the code file and whenever I use scanf(), the size of the file comes dangerously close to our limit. Finally, everything up to this point works fine so unless you see something that is horribly wrong, it's not my primary concern to change any of the code that I already have.

With that out of the way, I want to ask if anyone can point me in the right direction as to how to go about sorting the letters of each word in alphabetical order. I know I can use the same while loop to split the string into separate words but I'm just at a complete loss as to how to code the function to sort the letters alphabetically. I don't just want the code either but rather, an explanation as to how to do it first and if I can't figure it out, I'll come back. If anyone can help me out, I'd greatly appreciate it.

What about it doesn't make sense? Rather than having "return 0;" at the end of the program, causing it to shut down once all of the code has been run through, the program returns back to the beginning, asking for the user to input a new string, over and over again, until the user decides to shut it down. If that still doesn't make sense, I don't really know how to make it any clearer but either way, that doesn't really relate to my problem as I mentioned in my first post, the program is fully functional at this point sans the alphabetical sorting.

I am using embedded programming. I took some of the code out (just as I did in order to run it using a different compiler) but as I mentioned, that stuff is not really a big concern and it's something I can work on later, once the alphabetical sorting has been worked out. I haven't ever used qsort before (haven't had a need to really) so is it possible for you to explain that a little bit more? If not, I'll go ahead and Google it but I'm just guessing it would be much easier to understand if you were able to apply it to my situation specifically rather than just random pieces of code I find on the Internet.

Originally Posted by YPavluk

What about it doesn't make sense? Rather than having "return 0;" at the end of the program, causing it to shut down once all of the code has been run through, the program returns back to the beginning, asking for the user to input a new string, over and over again, until the user decides to shut it down. If that still doesn't make sense, I don't really know how to make it any clearer but either way, that doesn't really relate to my problem as I mentioned in my first post, the program is fully functional at this point sans the alphabetical sorting.

Ummm... no. The return value from a process is not a shutdown code, and it's silly to think it is. In fact, it represents a fundimental misunderstanding of how C programming works.

It's the loop that keeps your program running not the absence of a return value.

Operating Systems *expect* an integer return value, which generally represents an errorlevel... we return 0 to say "no errors"... void main() is a hang over from a wildly outdated, non-standard (even then) compiler that seems not to want to die. You should always use the correct form of ...

Code:

int main (void)
  {
     // your code

     return 0;  // or an error code
}

If you want your program to keep running, make sure the final return statement is outside your loop.

Originally Posted by CommonTater

Ummm... no. The return value from a process is not a shutdown code, and it's silly to think it is. In fact, it represents a fundimental misunderstanding of how C programming works.

It's the loop that keeps your program running not the absence of a return value.

Operating Systems *expect* an integer return value, which generally represents an errorlevel... we return 0 to say "no errors"... void main() is a hang over from a wildly outdated, non-standard (even then) compiler that seems not to want to die. You should always use the correct form of ...

Code:

int main (void)
  {
     // your code

     return 0;  // or an error code
}

If you want your program to keep running, make sure the final return statement is outside your loop.

I realize that return 0; is not a shutdown code, and if I made it seem like that, I apologize. I'm not as experienced with coding as I'm sure most of you are but I do understand that return 0; resulting in a shutdown is related to the operating system expecting a returned value rather than it being a shutdown code. However, as I mentioned in an earlier post, I am dealing with embedded programming that does not have an operating system so returning a value would be pointless. In addition to that, we were specifically told to use void main(void) and not to return a value. If I had a choice, I'd be using int main(void) as I have in the past but I don't have a choice so I'm just following directions.

Anyways, apparently, qsort is not available, just as laserlight mentioned. Is there any way to achieve the same result (sorting letters in a string alphabetically) without the use of qsort or other similar functions included in stdlib?