In Class: Week 1, Wednesday and Friday

In your cs21 subdirectory create a directory named 'class' and cd into that directory, and then make a directory named 'week01' and cd into that directory:

# cd into your cs21 subdirectory:
% cd            
% cd cs21       
% pwd	          
  /home/your_user_name/cs21

% mkdir class   
% cd class      
% pwd		
  /home/your_user_name/cs21/class

% mkdir week01  
% cd week01
% pwd           
  /home/your_user_name/cs21/class/week01

Now copy over all the files from my public/cs21/week01 directory into your week01 directory (remember to add the dot as the destination of the cp command). From your week01 directory:

% cp ~newhall/public/cs21/week01/* .
% ls

We are going to start by looking at the firstProg.py program together, so go ahead and open it in vim:
```
% vim firstProg.py  
```
To run the program in the python interpreter:
```
% python firstProg.py
```
Try modifying the firstProg.py in vim to print out a different string, and run it.
Next we will look at add.py. This program follows the general pattern that all (most) programs follow:
1. input phase: get data values for program variables
2. compute phase: do something with the program's data (some operations on variables and values)
3. output phase: display the results to the user

Running Python Programs

You can run your python program in the python interpreter two different ways:

Have the interpreter run your program to completion:
```
% python firstProg.py
```
Run the interpreter in interactive mode on your program (the python interpreter will continue to run after running your program, and you can enter new python commands at the prompt >>>:
```
% python -i firstProg.py
  >>>
  >>> print "hello there"
  hello there 
  >>>
```

To exit the python interpreter hold down the control and the D keys together (CNTL-D)

You can also just start the python interpreter in interactive mode without giving it a python code file to run:

  % python
  >>>