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Workshop 2: Conditions, Loops, Basic Formatting, and Standard Library Functions
BEFORE this and every workshop session,
you're strongly encouraged to think how you would do it.
You are not expected to have developed and tested a perfect solution before
the workshop,
but you should at least scratch out your approach on paper.
In this workshop we'll develop a short system utility to print a simple calendar.
We have already seen that Linux and Apple's macOS operating systems
provide a standard utility, named cal, to print calendars.
We'll aim to develop a utility, named mycal,
that prints the same output (but initially, just for a single month).
prompt> cal
July 2024
Su Mo Tu We Th Fr Sa
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30 31
Note that, even though a calendar is a 2-dimensional grid
(suggesting that a 2-dimensional array is required),
the program can easily be written with a 1-dimdensional array,
or without any array at all.
From the information presented in lectures so far, we know:
- our programs commence execution in the main() function.
- values are stored in variables,
each of which has a datatype.
- we can test a variable's current value using conditional tests,
and then execute different statements using the
if and else keywords to control the flow within our programs.
- we can execute a sequence of statements a known (bounded) number of times
using for loops.
- we can print out simple values using the printf() function.
So, before the workshop session,
and before you start coding,
think how you can combine this (already known) information
to develop a solution.
EXTRA WORK (AFTER THE WORKSHOP)
As we do for the Labsheets,
we provide some optional advanced tasks,
which we term chili questions,
prefixed by one or more chilis:
🌶
The more chilis, the more difficult the task.
-
There's some required information that we haven't yet covered in lectures
(information we can get from our computer's operating system).
Try to identify that extra information.
Consider the file
first_day_of_month.c
whose function determines the first day (Sun, Mon, ...) of a requested month.
Identify the functions that are used to determine this information,
and read their documentation for your system.
-
We know that Linux utility programs can receive optional command-line arguments
to specify actions beyond their default actions.
In the case of the cal utility,
if two (optional) arguments are provided,
we are specifying the required month and year to be printed.
Assuming we receive the additional two command-line arguments,
which the C program receives as character strings,
we can 'convert' their string representations of integers to
integer values using the standard atoi() function.
Extend your program to detect optional command-line arguments,
and to print the requested calendar.
-
🌶
How could we support left-handers?
-
🌶🌶
Under both Linux and macOS,
the standard cal program highlights the current day in reverse video
using
ANSI terminal escape sequences.
Can you support that?
-
🌶
🌶
🌶
Extend your solution to replicate the actions of the
system-provided cal program
which can display all 12 months of the current year in a 3x4 grid:
prompt> cal -y
2024
January February March
Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa
1 2 3 4 5 6 1 2 3 1 2
7 8 9 10 11 12 13 4 5 6 7 8 9 10 3 4 5 6 7 8 9
14 15 16 17 18 19 20 11 12 13 14 15 16 17 10 11 12 13 14 15 16
21 22 23 24 25 26 27 18 19 20 21 22 23 24 17 18 19 20 21 22 23
28 29 30 31 25 26 27 28 29 24 25 26 27 28 29 30
31
....
-
Wow! What happened in September 1752?
(which you don't have to deal with!) :
prompt> cal 9 1752
September 1752
Su Mo Tu We Th Fr Sa
1 2 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
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