Topical Information

This program will help you develop a useful application from output, calculations (including modulo), and library functions. It is also a good place to use constants.

Program Information

Write a program that tells the user what time of day it is in 24-hour (military) time (AM-PM is an option below). This program will be unusual in that there will be no user input (excepting options). Simply output the time of day to the user and exit the program. Be sure to report the results neatly.

Hints:

• The time function from the time library actually returns the number of seconds since midnight of January 1, 1970 (Greenwich Mean Time or GMT). (And, YES, you must use only the time function from the ctime library as we've learned to use it before! This is where the modulo comes in, you see!)
• A day has 60*60*24 seconds in it.

People keep wanting to call the functions localtime and asctime from the standard C library ctime here. Just don't! The goal of this program is for you to code this process yourself! (And asctime leaves a mess behind you would probably forget to clean up even if you knew how!)

As an example, you might have the program interaction look something like:

$ ./time.out

                 Welcome to the Time-of-Day Program!!!

It is currently 12:59:59.

Thank you for using the ToDP!!

Endeavor to have a timely day!

$ ./time.out

                 Welcome to the Time-of-Day Program!!!

It is currently 13:0:9.

Thank you for using the ToDP!!

Endeavor to have a timely day!

$

(Note: Notice that the second time isn't terribly pretty. That's fine. If you want to fix it, see the option below.)

(Note: You'll find that the times are off by several hours. That's because they are the time in Greenwich, England — see the link above. Adjusting for this is an option below.)

Thought Provoking Questions

1. If you had a large number of inches (say 103054), how would you determine how many feet and inches there were after yards and miles had been accounted for ...but without going through those intermediate calculations to determine miles and yards! (Hint: There are 1 foot and 10 inches left.)
2. How does this relate to having a huge number of seconds and trying to calculate hours, minutes, and seconds without having to remove decades, years, months, weeks, and days first?

Be sure to look for any helpful resources you can in the notes on programming with ctime's time() function. You can never tell when something might come in handy!

This assignment is (Level 2).

Options

• Prettying-Up the Display

  Most users just giggle. But a few are actually freaked out or even dazed. It's nothing terrible. It's not even a big thing. But the lack of 0's on your minutes and seconds (hours if you'd like) is the culprit. People just can't seem to adjust completely to a time like 10:1:7 for some reason. *shrug*

  Add (Level 1) to display the time in a pretty format with leading 0's using a simple branch (as described in Chapter 3). This would make the second run above display the time as: 13:00:09.

  More Thought Provoking Questions

  1. How will you decide if a value needs a leading 0? Which values are they? (Hint: See Chapter 3.)
  2. If you don't need to print a leading 0, is there anything else to do? An alternative action?

• De-Internationalization

  Well, most of the time you hear that programs and applications are moving toward more internationalization — making sure that the software will work anywhere and everywhere it is run around the world. Well, even though 24-hour format is generally considered generic and should be well understood pretty much anywhere, folks in the US can't be bothered to think quite that much on a regular basis. They like their 12-hour format and they'll hear none of this weird 24-hour mess!

  Add (Level 2) to display the time in American format (AM-PM, that is) as well as 24-hour format. (Hint: This will also require a simple branch as from Chapter 3.) This would make the second run above display the time as: 13:0:9 (or 1:0:9 PM for the poor Americans). (Or something like that...*grin*)

  More Thought Provoking Questions

  1. Is noon AM or PM? What about midnight?
  2. Is midnight 24:00 or 0:00?
  3. How will you decide if a time is before noon? What action will you perform if a time is before noon? (Hint: See Chapter 3.)
  4. If a time is after noon, what action will be taken?
  5. When printing the time, what value(s) get printed first no matter if the time is before or after noon?
  6. When printing the time, what value gets printed last no matter if the time is before or after noon?

• Re-Internationalization

  But, in the sake of making things work around the world instead of just in Greenwich, England, let's localize the time reported to Chicago time (US Central).

  Add (Level 1) to adjust the time from Greenwich Mean Time to US Central Time. (Hint: Check out this page for examples of GMT vs CDT/CST.)

  More Thought Provoking Questions

  1. Is Greenwich ahead of us or after us? Does this indicate that we add or subtract the hours difference?
  2. What is the difference between CDT and CST? (What do they stand for?) Which are we right now? How does this affect the hours difference between here and Greenwich?
  3. If it were 3 AM in Greenwich, what time is it here? Is that what your calculations produce?
  4. The midnight-shift problem can be handled with a decision structure (like those in Chapter 3), but can much more simply be handled by remembering how many hours there are in a day... (*ahem* modulo *ahem*)
     In fact, add an extra (Level 0.5) to adjust the time arithmetically instead of using a decision structure.

• Time Is As Time Does

  Most users want a single utility that can handle all of their needs. And since our little clock does the time of day, they'd also like to know what that day is.

  Add (Level 4) to also print out the current date (day, month, and year). (Hint: This will entail using those seconds you arbitrarily removed before and breaking them down. But our calendar's months are not quite amenable to modulo manipulation... Maybe some sort of decision structure like those in Chapter 3 would be of help..?)

  More Thought Provoking Questions

  1. If time is based in 1970, what year is that in the system that time(nullptr) implements? (Hint: It is NOT 1970!)
  2. Which seconds that we threw away before will we be needing to tell the month and day of this year?
  3. How many months are there in a year?
  4. How many days are there in each month?
  5. How can you tell if a year is a leap year? (Hint: It is NOT simply 'if the year is divisible by 4'.)
  6. What month(s) is(are) affected when this year is a leap year? (Hint: Be careful... What day of the month is it?)
  7. Did you decide to use sequential if's, cascaded if's, or a switch to make your month break-down? Why? Why not the others?

Total Level Possible

If you did all above options, this lab could be worth as much as (Level 10.5).