# Chapter 4. Integer Expressions

In This Chapter

• Declaring variables

• Creating expressions

• Decomposing compound expressions

• Analyzing the assignment operator

• Incrementing variables with the unary operator

In this chapter, you will be studying integer declarations and expressions. Algebra class introduced you to the concepts of variables and expressions. The teacher would write something on the board like

`x = 1`

This defines a variable `x` and sets it equal to the value 1 until some subsequent statement changes it for some reason. The term `x` becomes a replacement for 1. The teacher would then write the following expression:

`y = 2x`

Because I know that `x` is 1, I now know that `y` is equal to 2. This was a real breakthrough in the seventh grade. All conventional computer languages follow this same pattern of creating and manipulating variables.

# Declaring Variables

An integer variable declaration starts with the keyword `int` followed by the name of a variable and a semicolon, as in the following example:

`int n1;        // declare a variable n1`

All variables in C++ must be declared before they can be used. A variable declaration reserves a small amount of space in memory, just enough for a single integer, and assigns it a name. You can declare more than one variable in the same declaration, as in the following example, but it's not a good idea for reasons that will become clear as you work through subsequent chapters:

`int n2, n3;    // declare two variables n2 and n3`

### Note

A keyword is a word that has meaning to C++. You ...

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