# Chapter 2. Variables, Expressions, and Statements

One of the most powerful features of a programming language is the ability to manipulate variables. A variable is a name that refers to a value.

# Assignment Statements

An assignment statement creates a new variable and gives it a value:

julia> message = "And now for something completely different"
"And now for something completely different"
julia> n = 17
17
julia> π_val = 3.141592653589793
3.141592653589793

This example makes three assignments. The first assigns a string to a new variable named message, the second assigns the integer 17 to n, and the third assigns the (approximate) value of $pi$ to π_val (\pi TAB).

A common way to represent variables on paper is to write the name of each with an arrow pointing to its value. This kind of figure is called a state diagram because it shows what state each of the variables is in (think of it as the variable’s state of mind). Figure 2-1 shows the result of the previous example.

# Variable Names

Programmers generally choose names for their variables that are meaningful—they document what the variable is used for.

Variable names can be as long as you like. They can contain almost all Unicode characters (see “Characters”), but they can’t begin with a number. It is legal to use uppercase letters, but it is conventional to use only lowercase for variable names. ...

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