structs.c

/* This is a very commented piece of code so beginners at C/C++ can
 * hopefully understand how they work :) */

#include <stdio.h>

/* the struct keyword is almost like typedef.  You make the base struct and give
 * it a name, then you actually use that struct to create others that inherrit
 * the same variables that are inside of it.  Here we make a structure called
 * "time", that contains the hour, minute, and seconds... it holds the info for
 * all of the other structs we will declare that is of the same type. */
struct time
{
    int hour;
    int minutes;
    int seconds;
};


int main(void)
{

    /* prototype for the function timeUpdate.  It will return a struct */
    struct time timeUpdate(struct time now);


    /* This is declaring that the structs currentTime and nextTime are of
     * the type "time", so they inherit all of the qualities of the
     * time struct */
    struct time currentTime, nextTime;

    /* Get the current time and put it into the struct "currentTime" */
    printf("Enter the time (hh:mm:ss): ");
    scanf("%i:%i:%i", &currentTime.hour,
            &currentTime.minutes, &currentTime.seconds);

    /* Run a function that will update the time, passing it
     * the current time, and the function will return a structure...
     * that will equal "nextTime".  Makes sense if you think about it
     * remember that "nextTime" has been declared on line 22 and it has
     * all of the qualities of the global struct "time" that was declared
     * at the very beginning of the code. */
    nextTime = timeUpdate(currentTime);

    /* Of course, this is just printing out the nextTime. */
    printf("Updated time is %.2i:%.2i:%.2i\n", nextTime.hour,
                nextTime.minutes, nextTime.seconds);

    return 0;
}

/* function to update the time by one second and the structure that is
 * passed to the function timeUpdate is reffered to as "now" */

struct time timeUpdate (struct time now)
{
    ++now.seconds;
    if(now.seconds == 60){
        now.seconds = 0;
        ++now.minutes;

        if(now.minutes == 60){
            now.minutes = 0;
            ++now.hour;

            if(now.hour == 24)
                now.hour = 0;
        }
    }

    /* You can see that this function is of the type "struct time", so it is
     * going to RETURN a structure that holds the same contents of time...
     * of course, the struct "now" has been changed by all of the if statements
     * above. (this is what makes one more second on the "clock" so to speak */
    return now;
}