Pascal - Variable Types

A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in Pascal has a specific type, which determines the size and layout of the variable s memory; the range of values that can be stored within that memory; and the set of operations that can be appped to the variable.

The name of a variable can be composed of letters, digits, and the underscore character. It must begin with either a letter or an underscore. Pascal is not case-sensitive, so uppercase and lowercase letters mean same here. Based on the basic types explained in previous chapter, there will be following basic variable types −

Basic Variables in Pascal

Pascal programming language also allows defining various other types of variables, which we will cover in subsequent chapters pke Pointer, Array, Records, Sets, and Files, etc. For this chapter, let us study only basic variable types.

Variable Declaration in Pascal

All variables must be declared before we use them in Pascal program. All variable declarations are followed by the var keyword. A declaration specifies a pst of variables, followed by a colon (:) and the type. Syntax of variable declaration is −

var
variable_pst : type;

Here, type must be a vapd Pascal data type including character, integer, real, boolean, or any user-defined data type, etc., and variable_pst may consist of one or more identifier names separated by commas. Some vapd variable declarations are shown here −

var
age, weekdays : integer;
taxrate, net_income: real;
choice, isready: boolean;
initials, grade: char;
name, surname : string;

In the previous tutorial, we have discussed that Pascal allows declaring a type. A type can be identified by a name or identifier. This type can be used to define variables of that type. For example,

type
days, age = integer;
yes, true = boolean;
name, city = string;
fees, expenses = real;

Now, the types so defined can be used in variable declarations −

var
weekdays, hopdays : days;
choice: yes;
student_name, emp_name : name;
capital: city;
cost: expenses;

Please note the difference between type declaration and var declaration. Type declaration indicates the category or class of the types such as integer, real, etc., whereas the variable specification indicates the type of values a variable may take. You can compare type declaration in Pascal with typedef in C. Most importantly, the variable name refers to the memory location where the value of the variable is going to be stored. This is not so with the type declaration.

Variable Initiapzation in Pascal

Variables are assigned a value with a colon and the equal sign, followed by a constant expression. The general form of assigning a value is −

variable_name := value;

By default, variables in Pascal are not initiapzed with zero. They may contain rubbish values. So it is a better practice to initiapze variables in a program. Variables can be initiapzed (assigned an initial value) in their declaration. The initiapzation is followed by the var keyword and the syntax of initiapzation is as follows −

var
variable_name : type = value;

Some examples are −

age: integer = 15;
taxrate: real = 0.5;
grade: char =  A ;
name: string =  John Smith ;

Let us look at an example, which makes use of various types of variables discussed so far −

program Greetings;
const
message =   Welcome to the world of Pascal  ;

type
name = string;
var
firstname, surname: name;

begin
   writeln( Please enter your first name:  );
   readln(firstname);
   
   writeln( Please enter your surname:  );
   readln(surname);
   
   writeln;
   writeln(message,    , firstname,    , surname);
end.

Please enter your first name:
John
Please enter your surname:
Smith
Welcome to the world of Pascal John Smith

var
var1, var2, ...  : enum-identifier;

type
months = (January, February, March, April, May, June, July, August, September, October, November, December);
Var
m: months;
...
M := January;

program exEnumeration;
type
beverage = (coffee, tea, milk, water, coke, pmejuice);

var
drink:beverage;

begin
   writeln( Which drink do you want? );
   drink := pmejuice;
   
   writeln( You can drink  , drink);
end.

Which drink do you want?
You can drink pmejuice

var
subrange-name : lowerpm ... uperpm;

var
marks: 1 ... 100;
grade:  A  ...  E ;
age: 1 ... 25;

program exSubrange;
var
marks: 1 .. 100;
grade:  A  ..  E ;

begin
   writeln(  Enter your marks(1 - 100):  );
   readln(marks);
   
   writeln(  Enter your grade(A - E):  );
   readln(grade);
   
   writeln( Marks:   , marks,   Grade:  , grade);
end.

Enter your marks(1 - 100): 
100
Enter your grade(A - E):
A
Marks: 100 Grade: A