Thread: How to sort string with both alpha and number?

I store a string of both letters and numbers in the array.
Eg. ABC123, XYZ456.
However i want to sort by the numerical part only.
How can i do that? I try using isdigit() but i doesn't work.

Code:

void selectionSort(int arr[])
{
    int i, start, min, temp;


    for (start = 0; start < 10 -1; start++)
    {
        
        min = start;
        for (i = start+1; i < 10; i++) 
            if (isdigit (arr[i]) < isdigit (arr[min]) ) 
                min = i;


        temp = arr[start];
        arr[start] = arr[min];
        arr[min] = temp;
    }
}

Is there a known pattern to this... eg. Is it always 3 letters before the number?

If so it's pretty easy to start at an offset into the string...
Is digit simply says "yes" or "no" to the question, it doesn't return a comparable value, you need to to a little bit more work for that.


Assuming 3 letters...

Code:

if (atoi(&arr[i][3]) < atoi(&arr[min][3]))
  { ...

Originally Posted by CommonTater

Assuming 3 letters...

Code:

if (atoi(&arr[i][3]) < atoi(&arr[min][3]))
  { ...

Yup there is pattern to it. Eh it works now. but i dont really understand the way you do it. why & is required in this case? I didnt use atoi before. I thought its just convert string to integer, why does it help separate the letters and numbers?

The & gives the address of the first digit, to atoi(), which then will take all the digits, and as you stated, "turn the alpha into an integer". After doing that for two entries, the larger number can be determined, and the sorting can be done.

Originally Posted by wonderwall

Yup there is pattern to it. Eh it works now. but i dont really understand the way you do it. why & is required in this case? I didnt use atoi before. I thought its just convert string to integer, why does it help separate the letters and numbers?

Try this...

Code:

#include <stdio.h>

int main (void)
  {  int i;
     char arr[15] = "This is a test";

     for ( i =0; i < 16; i++)
        printf("%s\n", &arr[i]);

     return 0;
}

Get it now? The offset simply tells it where to start looking at the string (You don't always have to start at the beginning)... in your case I assumed 3 letters followed by 1 or more digits... so I started looking at the string's 4th character (arr[i][3]) for atoi().

Originally Posted by CommonTater

Try this...

Code:

#include <stdio.h>

int main (void)
  {  int i;
     char arr[15] = "This is a test";

     for ( i =0; i < 16; i++)
        printf("%s\n", &arr[i]);

     return 0;
}

Get it now? The offset simply tells it where to start looking at the string (You don't always have to start at the beginning)... in your case I assumed 3 letters followed by 1 or more digits... so I started looking at the string's 4th character (arr[i][3]) for atoi().

Thanks! I finally got it!