Variables and Types

Data types

C++ provides a rich set of built-in as well as user defined data types. Following table lists down seven basic C++ data types:

Built-in

• Boolean - boolean - either true or false
• Characters - alphabets and all the symbols. Defined using char.
• Integers - whole numbers which can be both positive and negative. Defined using int (4 bytes) or short int (2 bytes) or long int (8 bytes) based on the size of the numbers used.
• Floating point numbers - real numbers (numbers with fractions). Defined using float and double.
• Valueless using the void keyword
• Wide character using the wchar_t keyword

Type Modifiers

The above types can be modified using the following type modifiers: signed and unsigned short and long

User defined

• Structures - struct will be explained later, in the Structures section.
• Classes - class will be covered later, in the Classes section

C++ allows an array of characters to define strings. It also provides an extensive string library for manipulating strings and will be explained in the Strings section.

Typdefs

Typedefs allow for creating new names (think of them as aliases) for existing types. Following is the simple syntax to define a new type using typedef:

typedef int counter;
counter tick_c = 100;  // tick_c is a valid integer variable

Enumerated types

To create an enumeration requires the use of the keyword enum. The general form of an enumeration type is:

enum enum_name { list of names } var_list;

Above, the enum_name is the enumeration's type name. The list of names is comma separated.

For example, the following code defines an enumeration of colors called colors and the variable a_colour of type color. Finally, a_colour is assigned the value "green".

enum colour {red, green, blue} a_colour, another_colour;
a_colour = green;  // a_colour will be assigned value of '1'

Defining variables

For numbers, we will usually use the type int, which an integer in the size of a "word" the default number size of the machine which your program is compiled on. On most computers today, it is a 32-bit number, which means the number can range from -2,147,483,648 to 2,147,483,647 (same as long).

To define the variables foo and bar, we need to use the following syntax:

int foo;
int bar = 1;

The variable foo can be used, but since we did not initialize it, we don't know what's in it. The variable bar contains the number 1.

Now, we can do some math. Assuming a, b, c, d, and e are variables, we can simply use plus, minus and multiplication operators in the following notation, and assign a new value to a:

int a = 0, b = 1, c = 2, d = 3, e = 4;
a = b - c + d * e;
cout << a << endl; // will print 1-2+3*4 = 11

Exercise

In the next exercise, you will need to create a program which prints out the sum of the numbers a, b, and c.