Lab 6

Background

Pointers: stuff from lecture notes.

To keep track of time, computers need something to measure it against. In C on the lab computers, we get the number of seconds since 00:00:00 UTC on 1 January 1970.

As you might imagine, this produces a fairly large number -- it exceeds the bounds of a normal int. We therefore use a long int, which has twice the number of bits of a normal int. Our time.h library also defines a special data type to store the time value: time_t. On our computers, this is the same as a long int.

Technical details

Swapping data with pointers:

#include <stdio.h>

void swap(int *px, int *py) {
    int temp = *px;
    *px = *py;
    *py = temp;
}

int main() {
    int x = 1;
    int y = 2;
    printf("initial: %i %i\n", x, y);
    swap( &x, &y);
    printf("swapped: %i %i\n", x, y);
}

Watch out for the * and &

Getting the time:

#include <stdio.h>
#include <time.h>  // extra include

int main() {
    time_t now;
    now = time(NULL);

    long int a = now;
    printf("%li\n", now);
}

Your task...

Calling time(NULL) gives you a large integer. Use this value to calculate today's year, date, hours, and minutes.

Simplifying assumption: we pretend that each year has exactly 365 days. The 15th of March is therefore day 83 in year 2011. (use that date to figure out today's "day number")
(hint: how many seconds are there in a day?)
You cannot use struct for this assignment.
You cannot use any time-based functions from the standard library such as asctime or strftime.
You must use one function to calculate the day (pass in the total seconds, and a reference to the year and day).
You must use a separate function to calculate the hours and minutes. (again, pass the total seconds, and a reference to the hours and minutes)
You must use a separate function to print the time; this function can only take as arguments the year, day, hour, and minutes.






(optional: handle leap-years correctly, and print the month as
well)


... show your work to a demonstrator

Lab 6 for C programming

Exercise 14: Pointers

Background

Technical details

Your task...

... show your work to a demonstrator