itoa-recursive.c

#include <stdio.h>
#include <stdlib.h>

void aux_func(int n, char * buf, int radix, int i, int *len) {
  int q = n / radix;
  int r = n % radix;

  if (q < radix && q >=0 ) {
    *len = i + 2;
    *(buf+1) = r + '0';
    *(buf) = q + '0';
    *(buf+(*len)) = '\0';
    return;
  } else {
    aux_func(q, buf, radix, i + 1, len);
    *(buf + (*len - i) - 1) = r + '0';
  }

}

void itoa(int n, char * buf, int radix) {
  int len = 0;
  
  aux_func (n, buf, radix, 0, &len);
}


int main(int argc, char *argv[])
{
  int toBinary;
  
  scanf("%x", &toBinary);
  char binBuf[1024];
  char decBuf[1024];
  
  itoa(toBinary, binBuf, 2);
  printf("%s.\n", binBuf);
  
  itoa(toBinary, decBuf, 10);
  printf("%s.\n", decBuf);
  
  return 0;
}