Int to Binary Conversion explanation

Question

My question is based on this post: Decimal to Binary and it\'s chosen solution.

I can get the chosen answer code working, but it only works for 5 bits. How do I modi

Answer 1

void getBin(int num, char *str)
{
  *(str+8) = '\0';
  int mask = 0x80 << 1;
  while(mask >>= 1)
    *str++ = !!(mask & num) + '0';
}

main()
{
  char str[9];
  getBin(254, str);
  printf("%s\n", str);
  return 0;
}

For 8-bit number you need array of 9 chars. Also you need to change mask, so it can mask all bits.

The mask for the most significant bit for a 5-bit number like 11111 is 10000 which is equal to 16 decimal or 10 hexadecimal. Same thing for 8-bit number. The mask is 10000000. Since the loop start with mask >>= 1 the mask is shifted one to left int mask = 0x10 << 1; to compensate. Thus to modify it for a x-bit number, define an array of x+1 chars. Put \0 at index x. Find the x-bit number where the most significant bit of it is 1 and others are 0. The number is 2^(x-1) (2 power (x-1)).