Definition of a ‘Variable’

Different languages may differ slightly,

but the concept is the same as shown here.

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A “variable” is a letter or word that identifies a place
in the computer’s memory where data is stored.

Variable = expression

A variable can be used on the left side of the equal sign
in an assignment statement to store information
to be used later in the program.

X = 52
Amount = 12.34

A variable can be used on the right side of the equal sign
in an expression to retrieve information
that was previously stored in the computer’s memory.

Y = X / 2
Tax = Amount * .0775

However, sometimes expressions can be more complex

and there is some math to do, like 10 + 15.

Now we have to “do the math” and figure it out :

We add the two numbers in the expression to get one answer : 25.

Expressions always “resolve” into a single value.

Sometimes the math is a little harder to do, like the expression (7 + 3) * (2 + 3) ,

It may be convenient to think of variables as a way to substitute a name for a value.

For example :

Program Line	What does the program line do ?
Price = 100		The program assigns the value 100 to the variable ‘Price’ and stores the value 100 in memory.
Tax = .0775		The program assigns the value .0775 to the variable ‘Tax’ and stores the value .0775 in memory.
Total = Price * Tax		The program looks up the values stored at locations in memory called Price * Tax and calculates the value of the expression. The program then assigns the calculated value to the variable ‘Total’
PRINT Price , Tax, Total		Program looks up values stored in Price , Tax and Total, and displays or prints them.

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