Variables and Constants Chapter 2 Variables and Constants

Objectives Explain the different integer variable types used in C++. Declare, name, and initialize variables. Use character variables. Explain the different floating-point types and use variables of those types. Describe Boolean variables. Use constants.

Understanding Variables A variable is a data structure whose contents can change while a program is running. In C++ you must select the data type that best fits the nature of the data to be stored.

Integer Data Types An integer is a whole number. There are many ways to store integers; each has its own range and memory requirements. The integer data types in C++ are: char, unsigned char, short, unsigned short, int, unsigned int, long and unsigned long.

Declaring and Naming Variables Indicating to the compiler the name and type of variable you want to use is called “declaring” the variable. You must declare a variable for you can use it. A typical variable declaration might look like the follwing: int i; // declare i as an integer

Initializing Variables Initializing a variable means assigning a value to it. Variable values are indeterminate when they are first declared. You use the = sign to assign a value to a variable. A typical variable initialization statement might look like the following: i = 2; // initialize i to 2

Naming Variables Names of variables are called identifiers. Identifiers must start with a letter or an underscore (_). You can use letters, numerals, or underscores in the rest of the identifier. Use names that make the purpose of the variable clear. There can be no spaces in identifiers. Keywords cannot be used as identifiers.

Characters and the Char Data Type Characters are stored as numbers according to the ASCII codes. C++ includes a char data type for storing characters. Each variable of the char data type can hold only one character. A group of characters put together to form a word or phrase is called a string.

Floating-point data types Tasks such as working with money require floating-point data types. Floating-point data types can store fractional numbers. The floating-point data types in C++ are float, double and long double. With these types, you can also use exponential notation: 6.378164e6

Boolean Variables A Boolean variable can have two possible values. One value usually represents true and one usually represents false. Some C++ compilers do not support the Boolean data type.

Constants Constants hold data that does not change as the program runs. Constants must be given a data type and a name. An example of a statement that declares a constant: const double PI = 3.14159;

Summary Computers store data in data structures. Data is stored in variables or constants. Within one data type, there may be types with different ranges and memory requirements. Variables must be declared before they are used. Boolean variables can have one of two values.