Constant and Variable

Data items

Store data used in program:

• read in from user
• constants used in program

A data item can be declared either as a constant or a variable

• Constants are initialized with a value, but their value cannot be changed after that.
• The value of a variable can be changed as needed.

The keyword const in the declaration indicates that the data item is a constant

Example

void main()

{

// Declaring constants

const int MIN_VALUE = 0;

const int MAX_VALUE;              // Error

MIN_VALUE = 45;  // Error

cout << “MIN_VALUE is now “ <<   MIN_VALUE;

}

Declaration of data items.

We need to declare data items in our program prior to using them.

The declaration tells:

• whether the data item is a constant or a variable.
• the identifier that will be used in the program to name the data item.
• the data type for the data item.

Example

void main()

{

// Declaring a constant.

const float PI = 3.1416;

// Single variable declared at a time.

int         my_number;

float  GPA;

char      initial_letter;

// Can declare many data-items of the same type together.

int         height, base;

}