Raspberry Pi A, User Manual, Page: 199 / 314

C H A P T E R 1 2
A N I N T R O D U C T I O N T O P Y T H O N
183
when it prints integers and strings together. Finally, note that there is no division operation
(which would be indicated with the / symbol). This is because the example calculator program
uses
integers , which can only be whole numbers, with no decimal places or fractions allowed.
Although the calculation part of the program is now complete, it will run forever because
there is currently nothing to tell Python when it’s time to exit the loop. To provide the user
with a way to exit the program, add the following line:
goAgain = int(raw_input(“Type 1 to enter more numbers,
↵
or any other number to quit: “))
This allows the user to change the
goAgain
variable, which controls the
while
loop. If the
user enters the number
1
, the
goAgain
variable is still equal to
1
and the loop will run again.
However, if the user enters any other number, the evaluation is no longer true (
goAgain
is
no longer equal to
1
), and the loop will end.
The finished program should look like this, remembering that anything marked with ↵
should be entered onto a single line:
#!/usr/bin/env python
# Example 2: A Python program from the Raspberry Pi User Guide
userName = raw_input(“What is your name? “)
print “Welcome to the program,”, userName
goAgain = 1
while goAgain == 1:
firstNumber = int(raw_input(“Type the first number: “))
secondNumber = int(raw_input(“Type the second number: “))
print firstNumber, “added to”, secondNumber, “equals”,
↵
first secondNumber
print firstNumber, “minus”, secondNumber, “equals”,
↵
firstNumber - secondNumber
print firstNumber, “multiplied by”, secondNumber, “equals”,
↵
firstNumber * secondNumber
goAgain = int(raw_input(“Type 1 to enter more numbers, or
↵
any other number to quit: “))
Save the program as
calculator.py
, and run it by choosing Run Module from the Run
menu in IDLE or by typing
python calculator.py
at the terminal. Enter your user name
when prompted, and then provide the numbers that you want to calculate (see Figure 12-5)
until you get bored and then type anything other than 1 to exit the program.