Exercise 1 Basic C Program Development

NWEN 241 Exercise 1
(Basic C Program Development)

1 Objective
The objective of this exercise is to familiarise you with the C development tools used in
the course, write and compile your first C program, and learn how to debug C programs.
At the end of this exercise, you should submit the required files to the Assessment System
(https://apps.ecs.vuw.ac.nz/submit/NWEN241/Exercise_1) on or before the
submission deadline. You may submit as many times as you like in order to improve your
mark before the final deadline. Submissions beyond the deadline will not be marked and
will receive 0 marks.
2 Exercise Requirements
For NWEN 241, it is highly recommended that you undertake all development using the
computers in CO246. The computers in this lab use the Linux operating system. This
guide is written with the assumption that you are in CO246 lab.
If you are not able to go the lab, you can remotely access similar computers via secure
shell (ssh). Consult one of the remote study guides (see https://ecs.wgtn.ac.nz/
Courses/NWEN241_2023T1/RemoteStudyGuide) and follow one that suits you the
most.
3 Development Workflow
The development process is pretty simple and can be summarised into four major steps:
1. Edit source file using text editor of choice.
2. Compile source file in command line using gcc.
3. If bugs or warnings are present, debug and go back to step 1.
4. Run executable output file. If bugs are present, debug and go back to step 1.
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NWEN 241 2023-T1 (Basic C Program Development) Exercise 1
In Sections 4–7, we will go through each and every step of the workflow to get yourself
ready to work on the first set of programming exercises.
4 Editing Source Code
You may use any text editor to edit your source code. In this guide, we will use kate, a
no-frills text editor that is already installed in the CO246 lab computers. To open kate,
click on the Application Menu and type kate in the search bar. You should be able to see
Kate as an option in the menu.
Click on Kate. This should launch the text editor.
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NWEN 241 2023-T1 (Basic C Program Development) Exercise 1
Type the following simple C program in the text editor as is. (The above source code has
intentional errors. Do not fix them at this time.)
1 #include <stdio.h>
2
3 int main(void)
4 {
5 printf("Hello, world\n")
6 }
Save the file as hello.c. Your text editor window should look like this:
Note that after you saved the file to have the .c extension, kate automatically performed
syntax highlighting. This should make your coding and debugging easier.
5 Compiling on Command Line
You will now attempt to compile the hello.c program using gcc.
To do this, you will need to open a terminal that will enable you to invoke gcc. To open
a terminal, click on the Konsole button on the taskbar.
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NWEN 241 2023-T1 (Basic C Program Development) Exercise 1
This should launch a terminal window. You should now see something like this on your
desktop:
The terminal can be pretty scary at first, but once you become familiar with some
commands, you should be able to do your programming tasks easily. Section 9 lists
down some of the most important commands that you should know.
Let’s go back to what we want to do which is to compile hello.c using gcc. Before
doing this, ensure that the terminal is in the directory (folder) where the file hello.c
is located. By default, the terminal will open under your home directory. This is also
where you saved hello.c using kate (since you did not specify any directory to save
it). To confirm that the file is really in the current directory, type the command ls. This
command lists down all the files in the current directory.
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NWEN 241 2023-T1 (Basic C Program Development) Exercise 1
You should see hello.c in the listing, hence, we are now certain that the file is indeed
under the current directory. We can now proceed to compile it. To do this, type
gcc hello.c
in the terminal. You should see the following messages from the compiler:
When the compiler spits out error messages, it means that your source code has bugs that
need to be fixed.
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NWEN 241 2023-T1 (Basic C Program Development) Exercise 1
6 Debugging
If the compiler generates error messages, that means that your source code has bugs that
you need to fix. To debug your source code, read and understand the error messages
carefully.
In the above example, the error says that there is a missing semi-colon (;) before the
parenthesis. It even suggests where the semi-colon should be inserted. This gives you a
good clue on how to fix the code. Basically, you just have to insert a semi-colon at the end
of line 5 as follows:
1 #include <stdio.h>
2
3 int main(void)
4 {
5 printf("Hello, world\n");
6 }
Edit your source code to fix the problem and compile again.
As you can see, the compiler did not generate any error or warning message. That means
that it was successful and it generated an executable file.
7 Running the Executable File
When you invoke gcc as in
gcc hello.c
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NWEN 241 2023-T1 (Basic C Program Development) Exercise 1
it automatically names the executable file as a.out. If you run ls again in the terminal,
you should find the file a.out.
To run the program, type
./a.out
in the terminal.
It is good practice to explicitly name the executable file. You can do this by using the -o option
in gcc. To compile hello.c and generate hello as executable file, just type
gcc hello.c -o hello
in the terminal. To know more about the common gcc options, please refer to Section 9.
That completes the basic C development guide in Linux. You will now perform some
programming exercises that will require you to submit some files to the Assessment
System.
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NWEN 241 2023-T1 (Basic C Program Development) Exercise 1
8 Exercises
Activity 1: Basic I/O [10 Marks]
C uses the functions printf() and scanf() for basic output and input, respectively.
These functions can actually perform complicated formatting, but for this activity, you
will use them to acquire some input from the keyboard (referred to as standard input
or stdin in technical manuals) and display something to the monitor (referred to as
standard output or stdout in technical manuals).
We will talk about printf() and scanf() in the first tutorial-style lecture, but if you
want to start this exercise, you can refer to our reference materials for help on how to use
these functions.
For this activity, write a C program that performs the following:
1. Display the message "Enter an integer: " to stdout ( denotes a single
space character). Do not modify the message, otherwise, the automated marking
might not mark your work correctly.
2. Use scanf() to read input integer from stdin.
3. Display the input integer to stdout. Do not add any other string in the output,
otherwise, the automated marking might not mark your work correctly.
Save the program as activity1.c. Compile and run the program. If you are happy
with the program, submit it to the Assessment System for marking. Click on Run checks
to initiate auto-marking.
Activity 2: Basic I/O [10 Marks]
This is similar to Activity 1, except that you will now handle a string input without
whitespaces.
Write a C program that performs the following:
1. Display the message "Enter a string without whitespaces: " to
stdout ( denotes a single space character). Do not modify the message,
otherwise, the automated marking might not mark your work correctly.
2. Use scanf() to read input string from stdin.
3. Display the input string to stdout. (Do not add any other string in the output,
otherwise, the automated marking might not mark your work correctly.)
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NWEN 241 2023-T1 (Basic C Program Development) Exercise 1
Save the program as activity2.c. Compile and run the program. If you are happy
with the program, submit it to the Assessment System for marking. Click on Run checks
to initiate auto-marking.
Activity 3: Basic I/O [20 Marks]
This is similar to Activity 2, except that you will now handle any string input, even those
with whitespaces.
Write a C program that performs the following:
1. Display the message "Enter a string: " to stdout ( denotes a single space
character). Do not modify the message, otherwise, the automated marking might
not mark your work correctly.
2. Use scanf() to read input from stdin. Make sure that strings with whitespaces
are wholly captured.
3. Display the input string to stdout. (Do not add any other string in the output,
otherwise, the automated marking might fail.)
Save the program as activity3.c. Compile and run the program. If you are happy
with the program, submit it to the Assessment System for marking. Click on Run checks
to initiate auto-marking.
Activity 4: Basic I/O and Operators [20 Marks]
In this activity, you will use some C operators to perform a computation, and format a
floating point output using printf().
Write a C program that will convert an input temperature from Celsius to Fahrenheit.
The entire functionality should be implemented within the main() function. Follow this
guide to implement the program.
1. Declare a float variable ctemp which will hold the temperature in Celsius.
2. Declare another float variable ftemp which will hold the temperature in Fahrenheit.
3. Display the message "Enter temperature: " to stdout ( denotes a single
space character). Do not modify the message, otherwise, the automated marking
might not mark your work correctly.
4. Use scanf() to read input from stdin. Store the input in ctemp.
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NWEN 241 2023-T1 (Basic C Program Development) Exercise 1
5. Perform the actual conversion computation and assign the result to ftemp. Hint:
The formula for converting Celius to Fahrenheit is given by
tF =
9
5
tC + 32,
where tC is the temperature in Celsius, and tF is the temperature in Fahrenheit.
6. Display ftemp, to three decimal places, using the printf() function. (Do not add
any other string in the output, otherwise, the automated marking might fail.)
To verify your code is correct, you can try the following conversions:
• -20 Celsius is -4.000 Fahrenheit.
• 0 Celsius is 32.000 Fahrenheit.
• 100 Celsius is 212.000 Fahrenheit.
Save the program as activity4.c. Compile and run the program. If you are happy
with the program, submit it to the Assessment System for marking. Click on Run checks
to initiate auto-marking.
Activity 5: Functions [20 Marks]
In this activity, you will learn to write a C function.
Consider the following C program:
1 #include <stdio.h>
2
3 /* function implementation of calculate_area(length, width) */
4 // write your implementation here (you can use multiple lines)
5 /* end function implementation */
6
7 int main(void)
8 {
9 float l, w, a;
10 scanf("%f %f", &l, &w);
11 a = calculate_area(l, w);
12 printf("%f", a);
13 }
Complete the above program, providing an implementation of calculate_area()
which returns the product of the input parameters length and width. (Do not change
the other parts of the program.)
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NWEN 241 2023-T1 (Basic C Program Development) Exercise 1
Save the program as activity5.c. Compile and run the program. If you are happy
with the program, submit it to the Assessment System for marking. Click on Run checks
to initiate auto-marking.
Activity 6: Function-Like Macro [20 Marks]
In this activity, you will learn to write a C function-like macro.
Consider the following C program:
1 #include <stdio.h>
2
3 /* function-like macro implementation of SUM(A,B) */
4 // write your implementation here
5 /* end function-like macro implementation */
6
7 int main(void)
8 {
9 int a, b, s;
10 scanf("%d %d", &a, &b);
11 s = SUM(a, b);
12 printf("%d", s);
13 }
Complete the above program, providing an function-like macro implementation of
SUM() which returns the sum of the input parameters A and B. (Do not change the other
parts of the program.)
Save the program as activity6.c. Compile and run the program. If you are happy
with the program, submit it to the Assessment System for marking. Click on Run checks
to initiate auto-marking.
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NWEN 241 2023-T1 (Basic C Program Development) Exercise 1
9 Important Terminal Commands
The table below lists down the key commands that you should know to easily navigate
the Linux file system using the command line interface or terminal:
Command Purpose
ls List the contents of the current directory
pwd Print current working directory
cd Change to home directory
cd <dir> Change to directory <dir>
cd .. Change to parent directory
mkdir <dir> Create new directory <dir>
rm <file> Delete <file>
rm -r <dir> Delete directory <dir>
cp <f1> <f2> Make a copy of file <f1> called <f2>
mv <f1> <f2> Rename file <f1> to <f2>
10 Getting Help Using Manual Pages
If you want to know more about a particular command, you can use the man command
(which stands for manual). For instance, to know more about the command ls, just type
man ls
in the terminal.
Many of the functions in the standard C library also have their own manual pages. The
manual pages of C functions are usually in section 3. For instance, to view the manual
page of printf, just type
man 3 printf
in the terminal. The parameter 3 in the above command tells the terminal that you want
to see section 3 of the manual page.
11 GCC Options
The gcc compiler accepts many command-line options. The important options that you
have to know are as follows:
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NWEN 241 2023-T1 (Basic C Program Development) Exercise 1
Option Purpose and Example
-o <output-file-name>
Specify the filename of the output executable file
Example:
gcc hello.c -o hello
compiles hello.c and generates the executable file
hello if successful.
-Wall
Show all warnings
Examples:
gcc -Wall hello.c
gcc -Wall hello.c -o hello
-Werror
Changes warnings to errors (compilation will not
complete, no executable file will be generated).
This is a good option to use to force yourself to fix
warnings.
Examples:
gcc -Werror hello.c
gcc -Werror hello.c -o hello
-g
Compile with debugging flags enabled. This is needed
for debugging the executable file using gdb.
Examples:
gcc -g hello.c
gcc -g hello.c -o hello
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