Defining Variables

When you do long calculations, it is often convenient to give names to your intermediate results. Just as in standard mathematics, or in other computer languages, you can do this by introducing named variables.

This sets the value of the variable x to be 5:
Click for copyable input
Whenever x appears, the Wolfram Language now replaces it with the value 5:
Click for copyable input
This assigns a new value to x:
Click for copyable input
pi is set to be the numerical value of to 40digit accuracy:
Click for copyable input
Here is the value you defined for pi:
Click for copyable input
This gives the numerical value of , to the same accuracy as pi:
Click for copyable input
x=valueassign a value to the variable x
x=y=valueassign a value to both x and y
x=. or Clear[x]remove any value assigned to x

Assigning values to variables.

It is very important to realize that values you assign to variables are permanent. Once you have assigned a value to a particular variable, the value will be kept until you explicitly remove it. The value will, of course, disappear if you start a whole new Wolfram Language session.

Forgetting about definitions you made earlier is the single most common cause of mistakes when using the Wolfram Language. If you set x=5, the Wolfram Language assumes that you always want x to have the value 5, until or unless you explicitly tell it otherwise. To avoid mistakes, you should remove values you have defined as soon as you have finished using them.

Remove values you assign to variables as soon as you finish using them.

A useful principle in using the Wolfram Language.

The variables you define can have almost any name. There is no limit on the length of their names. One constraint, however, is that variable names can never start with numbers. For example, x2 could be a variable, but 2x means 2*x.

The Wolfram Language uses both uppercase and lowercase letters. There is a convention that builtin Wolfram Language objects always have names starting with uppercase (capital) letters. To avoid confusion, you should always choose names for your own variables that start with lowercase letters.

aaaaaa variable name containing only lowercase letters
Aaaaaa builtin object whose name begins with a capital letter

Naming conventions.

You can type formulas involving variables in the Wolfram Language almost exactly as you would in mathematics. There are a few important points to watch, however.

x y means x times y.
xy with no space is the variable with name xy.
5x means 5 times x.
x^2y means (x^2) y, not x^(2y).

Some points to watch when using variables in the Wolfram Language.