IC210 Lab 1


Part 0: Lab Ground Rules
Part 1: The Computing Environment

Login: Ubuntu

Your Unix Account

Part 2: Your First Program
We will be using the Unix environment to create, compile and execute C++ programs. First, you must choose a text editor to create your first C++ program:

Our C++ program (source code) will be entered as a file. This is the actual file that you will type using the editor. Other files will be used along with your source code to enable the execution of your program. For example, another type of file that may make up your project is a "header" file, or "include" file. An "include" file allows you to use additional source code that you or others have written. They comprise a library of helpful tools -- for example, they can provide input/output capabilities, standard math functions (like cosine, or finding the square-root), among others. In fact, they are often called standard library files. You reference a "header" file by "including" it into your source file. You will include a library file today that provides basic input and output services for your program (details to follow).

The complete collection of files needed to run our program is termed a project. So, a project is the collection of files that make up the program (or application) that you are developing.

Step-by-step instructions to creating the "HELLO WORLD" program

STEP
INFORMATION
0 Directory setup:
  • Open a terminal by selecting the Terminal application (Applications => Accessories => Terminal). This will open a window where you can type in Linux commands.
  • Make a new directory (what Windows calls a "folder") to hold your work. You use the "mkdir" command for this. In the terminal that you just opened, type exactly this:
    mkdir ic210
  • "Permissions" control who is allowed to view, modify, and use your files. Later you'll learn the details of this, but for now we just want to ensure that the permissions of your directory allow only you to use your files. The "chmod" (change file mode) command is used for this. First, you will change the permissions mode as follows: for users that belong to the same group(g) as this file or directory, you want to subtract permissions (a minus sign) for read(r), write(w), and execute(x). So enter this:
    chmod g-rwx ic210
    Next, you will do the same thing, but also for all "other"(o) users (all users that don't either own the file or belong to the same group). Enter this:
    chmod o-rwx ic210
  • If during this or any other step you get unexpected error messages, talk to your instructor.
  • Now we want to change the current directory to the new ic210 directory. The "cd" command changes the directory, so enter this:
    cd ic210
  • Make a new directory to hold your files for lab01:
    mkdir lab01
  • Change to this new directory:
    cd lab01
  • Let's verify that we are where we expect to be. Use the "pwd" command ("print what directory"). Enter this:
    pwd
    You should see a full listing of the "path" to your current working directory, which should look approximately like /home/mXXXXXX/ic210/lab01
  • NOTE: For all labs and other work with your Unix account, keep all of your files inside your ic210 folder. Inside the ic210 directory, make a new directory for each lab, homework, project, etc. Do this regardless of whether you are using a lab machine or your own Bancroft machine.
1 Open your preferred text editor (Applications => Accessories => "gedit Text Editor" or "GNU Emacs 23" or "GVim Text Editor" (the last one is known as "vi")). gedit is the simplest to start with.
2 The editor window is where you type in your source code.

The editor uses something called syntax coloring to make it easier for you to read the programs you have written. Syntax coloring highlights the different program elements such as comments, keywords, numbers, and variables. This allows you to easily identify elements of your source code and find common syntax mistakes quickly. For example, gedit highlights comments in blue. If you see your source code is blue then you likely forgot to close a comment block. Additionally, the editor attempts to help in other ways such as by providing automatic indenting, aligning braces, and so forth.

3 Create your main and add your include statements. If you do not understand what you are typing DO NOT BE CONCERNED. Your instructor will soon explain required and essential elements of C++ programs. Type the code exactly as shown below.
#include <iostream>

int main()
{
  std::cout << "Hello World!" << std::endl;
  return 0;
}
When done, save your file as follows:
  • From the menu, choose File => save (or select the save icon).
  • Navigate to the ic210/lab01 folder (you may need to select "Browse for other folders", find ic210, then find lab01).
  • Name your file main.cpp
4 Compile. If you want the programs you write to actually do something then you must compile them (turn source code into machine language). Converting high-level C++ source code into machine language is very complex, but compiler vendors solve this problem for you. To compile your program, first make sure that you have a terminal open from before, whose current directory is where you saved main.cpp. Once you are there, compile your program by typing into the terminal g++ -Wall -Wextra -c main.cpp.

If your program compiled successfully, you should not see any output from g++ as shown above and there should be a new file in your working directory called main.o. The new file contains the assembly language for your program and information about your program.

If you do see text output from g++, such as the example above, then get assistance from the instructor. If there are errors, they will be listed in the output. Tips for deciphering error messages are given at the end of this tutorial.

5 Link. Other files will be used along with your source code to enable the computer to execute the program. For example, another type of file that may make up your program is a "header" file, or "include" file. An "include" file allows you to use additional source code that you or others have written. They comprise a library of helpful tools -- for example, they can provide input/output capabilities, standard math functions (like cosine, or finding the square-root), among others. In fact, they are often called standard library files. You reference a "header" file by "including" it into your source file. You will include a library file today that provides basic input and output services for your program (details to follow). These additional files must be linked to yours in a process called linking. To do this, type g++ -o m012345 main.o in the terminal ("-o" is an argument that is used to specify the name of the output file, which is "m012345" in this case. "main.o" is the object file that you created above.).

6 Run! Once you successfully compiled and linked your program (no errors), then you are ready to execute your program. In your current working directory, you will see a new file called m012345 (or whatever you have named it). That is your program. To execute a file, type the file's name preceded by a "dot slash" (literally, "./") and hit the enter key.
Note: the "dot slash" is telling the computer to look for the program (m012345) in the current directory (indicated by the "dot"). In some cases you can get away with not including this, because your computer is set up to automatically look for commands in the current directory (amongst other places), but including the "dot slash" is safer because it will always work.
7 Program Output: Your program will output to the same terminal from where it was executed, as seen above.

Now, let's view the executable file you just executed. Type ls -l to list details of the contents of your current working directory. There is a file named main.cpp – it is your source code file. Note the size of the file (95 byes in our example). The file called m012345 is your program's executable file, which is combined with all of the other necessary machine code to run your program. Note the size (7782 bytes in our example)!! The increase in size is due to the code that was “included” or linked into your program. You should also see main.o listed, with a size in between the other two.

Part 3: Let's do it all over again!
You just accomplished quite a bit; you typed in a C++ program, compiled it and executed it. It is important that you understand all the steps involved, and that you are comfortable using a text editor and the terminal.

Repeat Part 2 of this lab all over again, with these changes:

// (Your name and alpha)
// This program adds two numbers

#include<iostream>

int main()
{
  int number1, number2, sum;
  number1 = 12;
  number2 = 13;
  sum = number1 + number2;
  std::cout << "The sum of these two integers is " << sum << std::endl;

  return 0;
}

Show your instructor when you finish this part.

Part 4: The "error" of your ways
When you make a certain kinds of common mistakes (syntax errors), the compiler won't be able to understand your program and will issue error statements in the terminal window. Each error message includes a number, which represents the line number of the error. Go to that line number to see where the problem is. Every syntax error must be corrected before a program will compile. Sometimes it is clear what's wrong, and other times you may have a hard time figuring out how to correct a syntax error. You will improve as you see enough errors to associate the messages with the syntax error. Here are a few simple rules and hints:

Experience and practice help a lot here. So for each of the below, purposefully make the syntax error in your current program and try to compile to see what the error message is. Correct the error before introducing the next error into your program:

Show your instructor when you finish this part.

Part 5: More on Linux

You'll spend the rest of your time learning more about Linux and the more powerful editors emacs/vi. Complete as many of the following steps as possible:

Part 6:Finishing Up

You should now be comfortable with being able to generate source code, compile it, execute the program, and correct basic syntax errors -- all in Linux. Let's clean up so you can get to your next class.

  • Click the Power button in the top right corner and…
  • Choose the Log Out option...
  • ...and an option window ("dialog box") will appear. Your options are to
    • Log Out
    • Cancel

LT J Schultz. Last modified by Assoc Prof. McDowell.

Valid XHTML 1.0 Transitional