Struct Example

struct.ino

struct hours_byte {
    unsigned int format: 1;     // range: 0-1, 0=24h 1=12h
    unsigned int ampm: 1;       // range: 0-1, 0=AM 1=PM
    unsigned int tenshours: 2;  // range: 0-2
    unsigned int hours: 4;      // range: 0-15 (guessing it never goes over 9)
};

void pHour(hours_byte when) {
   Serial.print(when.tenshours, DEC);
   Serial.print(when.hours, DEC);
   Serial.print(":00");
   if (when.format) Serial.print((char*)(when.ampm? "pm" : "am"));
   Serial.print(" == ");
   Serial.println(*(byte*)(hours_byte*)&when, BIN);
}

hours_byte now;

void setup() {
 
    // four in the afternoon, in 24hr format.
    now.tenshours = 1;
    now.hours = 6;
    now.format = 0;
    now.ampm = 0;
    pHour(now);
    
    // four in the afternoon, in 12hr format.
    now.tenshours = 0;
    now.hours = 4;
    now.format = 1;
    now.ampm = 1;
    pHour(now);
    
    // five in the morning, in 12hr format.
    now.tenshours = 0;
    now.hours = 5;
    now.format = 1;
    now.ampm = 0;
    pHour(now);
}

void loop() {}