Notes on the CS102 Lectures for Chapter 2

Put another way: READ THE BOOK! I know it's not the most gripping reading that you'll have this year, but wade your way through it -- it's good information.

Topics Covered In Class

• Basic Unix/Shell stuff: the commands ls, cat, mkdir, cd, cp, mv, rm and lynx. If you are using a Macintosh, use the "Terminal" command in the "Utilities" folder of the "Applications" folder. Macs are nice in that they have Unix integrated into their operating system. If you are using Windows, there are likely a bunch of options for running Unix. The one that I use is "Cygwin", available at www.cygwin.com. This is not a standard Unix, and has some quirks, but it's a good way for you to get practice with Unix on your laptop while you're in your dorm room or apartment. Finally, you can download vi for Windows at www.vim.org.

• File redirection and pipes: Unix has a wonderful feature that you can "redirect" the input and output of your programs. When a program reads from the terminal (for example, using cin), we say that it is "reading from standard input." When it writes to the terminal (for example, using cout), we say that it is "writing to standard output." You can "redirect" standard input from a file using the less-than sign, and you can "redirect" standard output to a file using the greater-than sign. For example, supose our "hello world" program is compiled into the file a.out, and we do the following:

  UNIX> a.out
  Hello World!
  UNIX> a.out > f.txt
  UNIX> cat f.txt
  Hello World!
  UNIX> cat < f.txt
  Hello World!
  UNIX> 
  

  You'll see that the second statement has "standard output redirected to the file f.txt".

  Note, if you don't give the program cat any arguments, it will read from standard input. So the second cat statement above takes "redirects standard input from f.txt."

  Finally, the vertical bar is called a "pipe". It is used to separate two commands, and to have standard output of the command to the left of the pipe go into standard input of the command to the right. For example:

  UNIX> a.out
  Hello World!
  UNIX>  a.out | cat -n
       1  Hello World
  UNIX>  a.out | cat -n | cat -n
       1       1  Hello World
  UNIX>  a.out | cat -n | cat -n | cat -n
       1       1       1  Hello World
  UNIX>
  

• Fun with vi: Using slash to find things. For example, did the Knicks win last night? Do:

  UNIX> lynx -dump http://www.nba.com/games/20070117/scoreboard.html > nba.txt
  

  then vi nba.txt and use slash to search for Knicks. Oh, they lost. Pity.

• A very basic and simple C++ program. This is the "hello world" program which I include below:

  // hw.cpp // Program to print out hello world. // Jim Plank #include < iostream > using namespace std; int main() { cout << "Hello World\n"; return 0; }

  Note, this differs from the book's first program in that I include the "using namespace std" line. This allows me to specify that I'm writing to cout rather than std::cout. Also note that I didn't go crazy with fifty comments like the book does. I'm an advocate for clean, clear, and sparse comments.

• Declaring integer variables and reading them with cin: Read the book for more explanation here. The book doesn't give a clear opinion on this, so I will: Put your variable declarations at the top of your code. You don't need to, but it makes your code far more readable, and that is important.

• Arithmetic operations and evaluation order: Again, read the book. Remember "mod" is remainder.

• Simple conditional expressions: "If" statements. Compound statements. Once again, read the book.

• More types: Floats and doubles.

• Practice Programs: Passing Ratings. The program in passing.cpp computes quarterback passing ratings, which follow a very weird formula, described by NFL.com in this document. Study it. One thing to notice about this program is that even though the inputs are really integers, I read them in as doubles so that the various averages and percentages would be calculated correctly.