char.c

#include <stdio.h>

//takes a string to read, a byte array to put stuff into, and the number of 
//bytes requested (strlen(input)/2)
void compute(char *input, int *into, int num) {
  int i;
  char buf[3]; buf[2] = '\0';

  for(i=0; i<num*2; i+=2) {
    buf[0] = input[i];
    buf[1] = input[i+1];
    into[i==0 ? 0 : i/2] = strtol(buf,0,16);
  }
}

int main(int argc, char **argv)
{
  if(argc < 2) {
    fprintf(stderr, "put the numbers as first argument.\n");
    return 1;
  }

  char *input = argv[1];

  //the number of bytes we want in the end
  int num = 6;
  //make the result array the correct size
  int result[num];

  //send the input to compute, which fills result with the numbers
  compute(input, &result[0], num);

  int i = 0;
  for(i = 0; i < 6; i++) {
    printf("%02x\n", result[i]);
  }

  return 0;
}