Enter, run and test the program

The last step in writing our program is also the first where we actually use the computer.

1. Within IDLE choose File → New Window and type in our three statement wonder.

temp_in_f = int(input())
temp_in_c = (temp_in_f - 32) * 5 / 9
print(temp_in_c)

2. Save the result (File → Save) into a file called f2c.py. Note how IDLE colourizes the program once it knows the file extension.

3. Press F5 to run your program. This will bring the Python shell window to the front where you will interact with your program.

4. Type 40 and then watch what number appears. If it isn't approximately 4 you've got a problem.

Step 4 is a test of our program but it isn't sufficient testing to be confident our program will work correctly with all possible values. We should try a couple of other known-correct values to be sure it works correctly. In later programs I'll have much more to say about choosing test values and testing procedures.

This is the core of our first Python program, but just the core. Now we have to attend to several other important issues:

• Naming values
• What will we see on the screen when we run the program?
• Documentation