Laboratory: Compiling C

Summary: We cover the basics of compiling C programs in a Linux environment.

Prerequisites: Familiarity with the MathLAN network. Familiarity with basic Linux commands. Ability to use an editor.

• Preparation
• Exercises
  • Exercise 1: Hello World
  • Exercise 2: A Second Program
  • Exercise 3: Choosing the Executable Name
  • Exercise 4: Errors

Preparation

a. Log in to your MathLAN workstation. (Of course, you've probably already done that if you're reading this laboratory.)

b. Open a terminal window into which you can type commands.

c. Create a directory for this lab. I would recommend csc161/labs/compiling-c.

Exercises

Exercise 1: Hello World

The first program that we often write in a new programming language is Hello World, which simply prints that string. Here is that program in C.

#include <stdio.h>

int
main ()
{
  printf ("Hello World\n");
  return 0;
} // main

a. Put that code into the file hello.c. You can use gedit to create the file. You can also use cat.

b. We compile files with the cc command. Type

cc hello.c

If all goes well, you should see no comments at all from the system.

However, you should find that the compilation created a file. Determine the name of that file.

c. As you may have just discovered, by default, the C compiler creates an executable file named a.out. You can run that file by typing

./a.out

Try doing so now.

Exercise 2: A Second Program

Create another simple C program that prints out some other message. Compile it and run it.

Exercise 3: Choosing the Executable Name

As you may have discovered, one disadvantage of the way C compiles files is that all executables end up with the same name, a.out. Fortunately, there is a flag you can give to the C compiler that tells it what output file name to use. In particular, you can write -o filename to choose the output file.

a. Type

cc -o hello hello.c

b. Verify that this created the file hello.

c. Run it with ./hello.

d. Do the same with the program you created in exercise 2.

Exercise 4: Errors

Try cutting out different parts of the program and see what happens when you try to compile it. For example,

• Drop the #include line.
• Leave out one of the sets of double quotation marks.
• Remove the f from printf.
• Remove the semicolon.
• Drop one of the braces.
• Change the spacing.