Binary to Hex Conversion

**elrookie** · 06-26-2007

Dear friends, I am trying to write a function that will convert an integer to a hex string. I would like to use the switch method. The code below is my work in progress, the logic i'm trying to follow is:

take the decimal integer 'n' and divide by 16
the remainder 'm' will form the first hex digit - hexstring[]
I want to use '0' to represent '1', '1' to represent 'A" and on until remainder 15 (F).
Then i want to take the quotient and divide by 16 and the remainder will form the second hex digit, next to last.
i want to repeat this process until my string is filled up and if it stop with a quotient equal to 0, fill the rest of the hex string with '0'.

Code:

int itox( char hexstring[], int n) {
   int m, b, flag;
   b = (m / 16);
   m = m - (b * 16);
   for (m = 0;m > 0; m++)
   switch (m) {

case '1' :
   m = 01; 
   break;

   case '2' : 
   m = 02;
   break;

   case '3' : 
   m = 03;
   break;

   case '4' :
   m = 04;
   break;

   case '5' : 
   m = 05;
   break;
   
   case '6' : 
   m = 06;    
   break;
   
   case '7' : 
   m = 07;
   break;
   
   case '8' : 
   m = 08;
   break;
   
   case '9' :
   m = 09;
   break;
   
   case '10' :
   m = A; 
   break;

   case '11' : 
   m = B;
   break;
   
   case '12' : 
   m = C;
   break;

   case '13' : 
   m = D;
   break;
   
   case '14' :
   m = E;
   break;
  
   case '15' : 
   m = F:
   break;
   
   default:
   flag = 0;
   break;
   }

  return (hexstring[m++]);
  }

}

could someone help me with my syntax, when I pass on a decimal i have an invalid digit "8" in octal constant

**maverickbu** · 06-26-2007

http://cboard.cprogramming.com/showthread.php?t=91184

**itsme86** · 06-26-2007

Why is the subject of this thread "binary to hex conversion"? Your function is screwy enough that I can't really tell what's going on, but it sounds like you just want:

Code:

char buffer[BUFSIZ];
sprintf(buffer, "&#37;X", n);

**elrookie** · 06-26-2007

sorry for the screw up code,

can't use printf because it is not allowed.

Code:

int itox( char hexstring[], int n) {    /* takes in an integer n */
   int m, b, flag;
   b = (m / 16);                               /* i divide by 16 */
   m = m - (b * 16);                        /* then because b is an int i can find the remainder by subtracting this number from the original number*/
   for (m = 0;m > 0; m++)              /* then i want to start a for loop saying if m is greater then zero, increment count by testing the cases below */
   switch (m) {                               */
/* finally after checking the cases, put them into a string and return that. */

if you have any better suggestiongs of how i should rewrite so is not so screwed up.

**vart** · 06-26-2007

where do you assign something to hexstring?
reminder operator is %
where do you use n?

**itsme86** · 06-26-2007

Some things to consider:

You're using m uninitialized. It starts off as garbage because you never give it an initial value.

Code:

b = (m / 16);  
m = m - (b * 16);

...can just be rewritten:

Code:

m = m &#37; 16;

b is unnecessary.

Next, your for loop will never run:

Code:

for (m = 0;m > 0; m++)

You initialize m to 0 and then the condition checks if m is greater than 0, which obviously it won't be. Your entire loop will just be skipped over.

This brings us to your switch statement. What if you simply did this instead:

Code:

char hexdigits[] = "0123456789ABCDEF";
hexstring[index++] = hexdigits[m];

As long as m is between 0 and 15 (inclusive), it will assign the correct hex digit to your hexstring.

Finally, don't forget to terminate hexstring with a '\0' after the loop to turn it into a string.

**mike_g** · 06-26-2007

Whats m? Unless it could be anything when you are calculating what b is since its not initialized.

To loop through the string you could pass a pointer to the string in eg:

Code:

int itox( char* hex_str)

You will then need to loop through all the characters in the string something like:

Code:

while(*hex_str)
{
    //get your hex value here
    *hex_str++;
}

If you want to split the char into 2 nibbles, then use the modulus operator like vart said. Eg:

Code:

left = this_char / 16;
right = this_char &#37; 16;

Hope that helps.

**elrookie** · 06-26-2007

thank you for your suggestions! a lot

I have a question about this piece of code:

Code:

char hexdigits[] = "0123456789ABCDEF";
hexstring[index++] = hexdigits[m];

where does index++ come from?

thanks for the suggestion Mike about the pointer but we haven't covered that in class yet, so I am not familiar with that method yet.

but how will it know that if it gets a remainder 11 it suppose to be B? because of the order of where it is position in the hexdigits [] ?

Code:

/* so far i got this i'll continue working on this to get what i want*/


int itox( char hexstring[], int m) 


{
   int m, flag;
   m = m &#37; 16;
   for (m = 0 ;; m++)
   char hexdigits[] = "0123456789ABCDEF"
   hexstring[index++] = hexdigits[m];
   {  
   return (hexstring[m]);
}

**itsme86** · 06-26-2007

It starts at 0, each time through the loop it just increments by 1. You just build the string one character at a time that way.

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