Code for question http://stackoverflow.com/questions/28404460/casting-of-char-in-ruby-is-different-in-c

test_printf.c

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

char * int2bin(int i)
{
  size_t bits = sizeof(int) * CHAR_BIT;

  char * str = malloc(bits + 1);
  if(!str) return NULL;
  str[bits] = 0;

  // type punning because signed shift is implementation-defined
  unsigned u = *(unsigned *)&i;
  for(; bits--; u >>= 1)
    str[bits] = u & 1 ? '1' : '0';

  return str;
}

int main() {
  char a = (char)129;

  printf("char: %c\n",a);
  printf("octal: %o\n",a);
  printf("hexa: %x\n",a);
  printf("unsigned: %u\n",a);
  printf("binary: %s\n",int2bin(a));

  printf("char: %c\n",129);
  printf("octal: %o\n",129);
  printf("hexa: %x\n",129);
  printf("unsigned: %u\n",129);
  printf("binary: %s\n",int2bin(129));

  return 0;
}