#include <stdint.h>

void foo(void) {
  int8_t  w;    // exactly 8 bits, signed
  int16_t x;    // exactly 16 bits, signed
  int32_t y;    // exactly 32 bits, signed
  int64_t z;    // exactly 64 bits, signed

  uint8_t w;    // exactly 8 bits, unsigned
  ...etc.
}