Thread: hex to decimal

Creating a program to convert hex to decimal is not difficult what-so-ever. Though, I'm unsure of how to convert a single hex character to decimal since I'm used to working in pairs. For instance 'FF' or '23'.

Just for a hint, here is how it works.

Step 1

Code:

Take the value of first hex character
Take an array and loop 16 times left shifting by four digits each time.
Note: If you do happen upon a hex value that you entered, break the loop.

Step 2

Code:

Take the value of the second hex character and add that to the previously obtained value.
Do this 16 times also with a loop.
Note: If you do happen upon a hex value that you entered, break the loop.

If you would like for me to show a sample example, I can.

Edit: You could use scanf() or sprintf() to get the %x. If so, you can always view this thread.

If you have further questions, please feel free to ask.


- Stack Overflow

I'd think you could roll your own with sscanf.

Code:

#include <stdio.h>

char *foo(char *dst, const char *src)
{
   int i, j = 0;
   for ( i = 0; src[i]; ++i )
   {
      if ( src[i] != '%' )
      {
         dst[j++] = src[i];
      }
      else
      {
         unsigned ch;
         if ( sscanf(&src[++i/* skip '%' */], "%2x", &ch) != 1 )
         {
            return NULL;
         }
         dst[j++] = ch;
         ++i; /* with the loop's increment, this will skip the 2 hex chars */
      }
   }
   dst[j] = '\0';
   return dst;
}

int main(void)
{
   const char text[] = "C%2B%2B%20or%20C%3F";
   char result [ sizeof text ];
   puts(text);
   if ( foo(result,text) )
   {
      puts(result);
   }
   return 0;
}

/* my output
C%2B%2B%20or%20C%3F
C++ or C?
*/