80. Register Bitfields Using Struct Overlay

#include <stdio.h>
#include <stdint.h>

typedef union {
    struct {
        uint8_t enable    : 1;
        uint8_t mode      : 2;
        uint8_t interrupt : 1;
        uint8_t reserved  : 4;
    } bits;
    uint8_t reg;
} ControlRegister;

int main() {
    uint8_t e, m, i;
    scanf("%hhu %hhu %hhu", &e, &m, &i);

    // Construct and print register value
    ControlRegister ctrl_reg = {0};
    ctrl_reg.bits.enable = e & 0x01;
    ctrl_reg.bits.mode = m & 0x03;
    ctrl_reg.bits.interrupt = i & 0x01;

    printf("%u", ctrl_reg.reg);
    return 0;
}