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Working with numbers

You can use variables to store numbers.

pocket_money = 20

The variable ‘pocket_money’ is used to store how much pocket money you have. Right now you have £20.

As well as using fixed numbers in calculations and storing the answer in a variable, we can also use variables within the calculations themselves. In this example, the instruction uses the variable ‘money_in_bank’ to calculate the answer and then stores the answer in a variable called ‘total_money’.

total_money = money_in_bank + 10

The variables represent any value we choose to assign to them.

Consider this Python (3.x) program:

>>> money_in_bank = 20
>>> total_money = money_in_bank + 10
>>> print(total_money)
30

The first line stores the value 20 to the variable ‘money_in_bank’. Since the computer knows that ‘money_in_bank’ has the value 20, it can calculate the value of ‘total_money’ and store it. Once calculated, the value of ‘total_money’ can be printed to the screen.

Once a value is stored, all sorts of mathematical operations can be performed on the variables:

>>> money_in_bank = 20
>>> total_money = money_in_bank + 10
>>> print(total_money)
30
>>> cost_of_holiday = 150
>>> left_to_pay = cost_of_holiday - total_money
>>> print(left_to_pay)
120

Working with text

A variable can hold a number, but it can also hold a piece of text. Just one letter is called a character. More than one character is called a string.

A text variable works in the same way as a number variable, with a couple of differences:

• text variables hold characters (letters, digits, punctuation)
• the data in text variables is placed in quotes
• arithmetic calculations cannot be performed on text variables

Consider the following Python (3.x) program that uses strings:

>>> message = "Hooray! It's my birthday!"
>>> print(message)
Hooray! It's my birthday!