Pascal tutorial

Pascal
ii
AbouttheTutorial
Pascal is a procedural programming language, designed in 1968 and published in
1970 by Niklaus Wirth and named in honor of the French mathematician and
philosopher Blaise Pascal. Pascal runs on a variety of platforms, such as Windows,
Mac OS, and various versions of UNIX/Linux.
This tutorial will give you great understanding of Pascal to proceed with Delphi
and other related frameworks etc.
Audience
This tutorial is designed for Software Professionals who are willing to learn Pascal
Programming Language in simple and easy steps. This tutorial will give you great
understanding on Pascal Programming concepts, and after completing this tutorial,
you will be at intermediate level of expertise from where you can take yourself to
higher level of expertise.
Prerequisites
Before proceeding with this tutorial you should have a basic understanding of
software basic concepts like what is source code, compiler, text editor, and
execution of programs, etc. If you already have understanding on any other
computer programming language, then it will be an added advantage to proceed.
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Pascal
i
TableofContents
About the Tutorial...................................................................................................................................ii
Audience.................................................................................................................................................ii
Prerequisites...........................................................................................................................................ii
Copyright & Disclaimer............................................................................................................................ii
Table of Contents.....................................................................................................................................i
1. OVERVIEW...........................................................................................................................1
Features of the Pascal Language .............................................................................................................1
Facts about Pascal...................................................................................................................................1
Why to use Pascal?..................................................................................................................................2
2. ENVIRONMENT SET UP........................................................................................................3
Installing Free Pascal on Linux.................................................................................................................3
Installing Free Pascal on Mac ..................................................................................................................4
Installing Free Pascal on Windows ..........................................................................................................4
Text Editor...............................................................................................................................................4
3. PROGRAM STRUCTURE........................................................................................................5
Pascal Program Structure........................................................................................................................5
Pascal Hello World Example....................................................................................................................6
Compile and Execute Pascal Program......................................................................................................7
4. BASIC SYNTAX......................................................................................................................9
Variable...................................................................................................................................................9
Functions/Procedures .............................................................................................................................9
Comments...............................................................................................................................................9
Case Sensitivity .....................................................................................................................................10
Pascal Statements .................................................................................................................................10

Pascal
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Reserved Words in Pascal .....................................................................................................................10
Character Set and Identifiers in Pascal ..................................................................................................10
5. DATA TYPES.......................................................................................................................12
Pascal Data Types..................................................................................................................................12
Type Declarations..................................................................................................................................12
Integer Types ........................................................................................................................................13
Constants..............................................................................................................................................13
Enumerated types.................................................................................................................................14
Subrange Types.....................................................................................................................................14
6. VARIABLE TYPES ................................................................................................................16
Basic Variables in Pascal........................................................................................................................16
Variable Declaration in Pascal ...............................................................................................................16
Variable Initialization in Pascal..............................................................................................................18
Enumerated Variables...........................................................................................................................19
Subrange Variables ...............................................................................................................................20
7. CONSTANTS.......................................................................................................................21
Declaring Constants ..............................................................................................................................21
8. OPERATORS.......................................................................................................................23
Arithmetic Operators ............................................................................................................................23
Relational Operators.............................................................................................................................24
Boolean Operators................................................................................................................................26
Bit Operators.........................................................................................................................................28
Operators Precedence in Pascal ............................................................................................................31
9. DECISION MAKING.............................................................................................................33
if-then Statement..................................................................................................................................34
Syntax ...................................................................................................................................................34

Pascal
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Flow Diagram ........................................................................................................................................35
Example ................................................................................................................................................35
if-then-else Statement ..........................................................................................................................36
Syntax ...................................................................................................................................................36
Flow Diagram ........................................................................................................................................36
Example ................................................................................................................................................37
The if-then-else if-then-else Statement.................................................................................................37
Syntax ...................................................................................................................................................38
Example ................................................................................................................................................38
Nested if-then Statements ....................................................................................................................39
Syntax ...................................................................................................................................................39
Example ................................................................................................................................................40
Case Statement.....................................................................................................................................41
Syntax ...................................................................................................................................................41
Flow Diagram ........................................................................................................................................42
Example ................................................................................................................................................42
Case Else Statement..............................................................................................................................43
Syntax ...................................................................................................................................................43
Flow Diagram ........................................................................................................................................44
Example ................................................................................................................................................44
Nested Case Statements .......................................................................................................................45
Syntax ...................................................................................................................................................45
Example ................................................................................................................................................45
10. LOOPS ...............................................................................................................................47
While-do Loops .....................................................................................................................................48
Syntax ...................................................................................................................................................48
Flow Diagram ........................................................................................................................................49

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Example ................................................................................................................................................49
For-do Loop...........................................................................................................................................50
Syntax ...................................................................................................................................................50
Example ................................................................................................................................................51
Repeat-Until Loop .................................................................................................................................52
Syntax ...................................................................................................................................................52
Flow Diagram ........................................................................................................................................53
Example ................................................................................................................................................53
Nested Loops ........................................................................................................................................54
Example ................................................................................................................................................55
Loop Control Statements: .....................................................................................................................56
Break Statement ...................................................................................................................................56
Syntax ...................................................................................................................................................57
Flow Diagram:.......................................................................................................................................57
Example ................................................................................................................................................57
Continue Statement..............................................................................................................................58
Syntax ...................................................................................................................................................58
Flow Diagram ........................................................................................................................................59
Example ................................................................................................................................................59
goto Statement .....................................................................................................................................60
Syntax ...................................................................................................................................................60
Flow Diagram ........................................................................................................................................61
Example ................................................................................................................................................61
11. FUNCTIONS .......................................................................................................................63
Subprograms.........................................................................................................................................63
Functions ..............................................................................................................................................63
Defining a Function ...............................................................................................................................63

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Function Declarations ...........................................................................................................................65
Calling a Function..................................................................................................................................65
12. PROCEDURES.....................................................................................................................67
Defining a Procedure.............................................................................................................................67
Procedure Declarations.........................................................................................................................68
Calling a Procedure ...............................................................................................................................68
Recursive Subprograms.........................................................................................................................69
Arguments of a Subprogram: ................................................................................................................71
Subprogram Call by Value .....................................................................................................................71
Subprogram Call by Reference ..............................................................................................................73
13. VARIABLE SCOPE ...............................................................................................................75
Local Variables ......................................................................................................................................75
Global Variables....................................................................................................................................76

Pascal
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Pascal is a general-purpose, high-level language that was originally developed by
Niklaus Wirth in the early 1970s. It was developed for teaching programming as a
systematic discipline and to develop reliable and efficient programs.
Pascal is Algol-based language and includes many constructs of Algol. Algol 60 is a
subset of Pascal. Pascal offers several data types and programming structures. It is
easy to understand and maintain the Pascal programs.
Pascal has grown in popularity in the teaching and academics arena for various
reasons:
 Easy to learn.
 Structured language.
 It produces transparent, efficient, and reliable programs.
 It can be compiled on a variety of computer platforms.
FeaturesofthePascalLanguage
Pascal has the following features:
 Pascal is a strongly typed language.
 It offers extensive error checking.
 It offers several data types like arrays, records, files, and sets.
 It offers a variety of programming structures.
 It supports structured programming through functions and procedures.
 It supports object oriented programming.
FactsaboutPascal
 The Pascal language was named for Blaise Pascal, French mathematician and
pioneer in computer development.
1. OVERVIEW

Pascal
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 Niklaus Wirth completed development of the original Pascal programming
language in 1970.
 Pascal is based on the block structured style of the Algol programming
language.
 Pascal was developed as a language suitable for teaching programming as a
systematic discipline, whose implementations could be both reliable and
efficient.
 The ISO 7185 Pascal Standard was originally published in 1983.
 Pascal was the primary high-level language used for development in the Apple
Lisa, and in the early years of the Mac.
 In 1986, Apple Computer released the first Object Pascal implementation, and
in 1993, the Pascal Standards Committee published an Object-Oriented
Extension to Pascal.
WhytousePascal?
Pascal allows the programmers to define complex structured data types and build
dynamic and recursive data structures, such as lists, trees and graphs. Pascal offers
features like records, enumerations, subranges, dynamically allocated variables with
associated pointers and sets.
Pascal allows nested procedure definitions to any level of depth. This truly provides
a great programming environment for learning programming as a systematic
discipline based on the fundamental concepts.
Among the most amazing implementations of Pascal are:
 Skype
 Total Commander
 TeX
 Macromedia Captivate
 Apple Lisa
 Various PC Games
 Embedded Systems

Pascal
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There are several Pascal compilers and interpreters available for general use. Among
these are:
 Turbo Pascal: provides an IDE and compiler for running Pascal programs on
CP/M, CP/M-86, DOS, Windows, and Macintosh.
 Delphi: provides compilers for running Object Pascal and generates native
code for 32- and 64-bit Windows operating systems, as well as 32-bit Mac OS
X and iOS. Embarcadero is planning to build support for the Linux and Android
operating system.
 Free Pascal: it is a free compiler for running Pascal and Object Pascal
programs. Free Pascal compiler is a 32- and 64-bit Turbo Pascal and Delphi
compatible Pascal compiler for Linux, Windows, OS/2, FreeBSD, Mac OS X,
DOS, and several other platforms.
 Turbo51: it is a free Pascal compiler for the 8051 family of microcontrollers,
with Turbo Pascal 7 syntax.
 Oxygene: it is an Object Pascal compiler for the .NET and Mono platforms.
 GNU Pascal (GPC): it is a Pascal compiler composed of a front end to GNU
Compiler Collection.
We will be using Free Pascal in these tutorials. You can download Free Pascal for your
operating system from the link: Download Free Pascal
InstallingFreePascalonLinux
The Linux distribution of Free Pascal comes in three forms:
 a tar.gz version, also available as separate files.
 a .rpm (Red Hat Package Manager) version.
 a .deb (Debian) version.
Installation code for the .rpm version:
rpm -i fpc-X.Y.Z-N.ARCH.rpm
2. ENVIRONMENT SET UP

Pascal
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Where X.Y.Z is the version number of the .rpm file, and ARCH is one of the supported
architectures (i386, x86_64, etc.).
Installation code for the Debian version (like Ubuntu):
dpkg -i fpc-XXX.deb
Where XXX is the version number of the .deb file. For details read: Free Pascal
Installation Guide
InstallingFreePascalonMac
If you use Mac OS X, the easiest way to use Free Pascal is to download the Xcode
development environment from Apple's web site and follow the simple installation
instructions. Once you have Xcode setup, you will be able to use the Free Pascal
compiler.
InstallingFreePascalonWindows
For Windows, you will download the Windows installer, setup.exe. This is a usual
installation program. You need to take the following steps for installation:
 Select a directory.
 Select parts of the package you want to install.
 Optionally choose to associate the .pp or .pas extensions with the Free Pascal
IDE.
For details read: Free Pascal Installation Guide
TextEditor
This will be used to type your program. Examples of few editors include Windows
Notepad, OS Edit command, Brief, Epsilon, EMACS, and vim or vi.
Name and version of text editor can vary on different operating systems. For
example, Notepad will be used on Windows and vim or vi can be used on windows as
well as Linux or UNIX.
The files you create with your editor are called source files and contain program
source code. The source files for Pascal programs are typically named with the
extension .pas.

Pascal
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Before starting your programming, make sure you have one text editor in place and
you have enough experience to write a computer program, save it in a file, compile
it and finally execute it.

Pascal
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Before we study basic building blocks of the Pascal programming language, let us
look a bare minimum Pascal program structure so that we can take it as a reference
in upcoming chapters.
PascalProgramStructure
A Pascal program basically consists of the following parts:
 Program name
 Uses command
 Type declarations
 Constant declarations
 Variables declarations
 Functions declarations
 Procedures declarations
 Main program block
 Statements and Expressions within each block
 Comments
Every Pascal program generally have a heading statement, a declaration and an
execution part strictly in that order. Following format shows the basic syntax for a
Pascal program:
program {name of the program}
uses {comma delimited names of libraries you use}
const {global constant declaration block}
var {global variable declaration block}
3. PROGRAM STRUCTURE

Pascal
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function {function declarations, if any}
{ local variables }
begin
...
end;
procedure { procedure declarations, if any}
{ local variables }
begin
...
end;
begin { main program block starts}
...
end. { the end of main program block }
PascalHelloWorldExample
Following is a simple pascal code that would print the words "Hello, World!":
program HelloWorld;
uses crt;
(* Here the main program block starts *)
begin
writeln('Hello, World!');
readkey;
end.
Let us look various parts of the above program:
 The first line of the program program HelloWorld; indicates the name of the
program.

Pascal
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 The second line of the program uses crt; is a preprocessor command, which
tells the compiler to include the crt unit before going to actual compilation.
 The next lines enclosed within begin and end statements are the main program
block. Every block in Pascal is enclosed within a begin statement and
an end statement. However, the end statement indicating the end of the main
program is followed by a full stop (.) instead of semicolon (;).
 The begin statement of the main program block is where the program
execution begins.
 The lines within (*...*) will be ignored by the compiler and it has been put to
add a comment in the program.
 The statement writeln('Hello, World!'); uses the writeln function available in
Pascal which causes the message "Hello, World!" to be displayed on the screen.
 The statement readkey; allows the display to pause until the user presses a
key. It is part of the crt unit. A unit is like a library in Pascal.
 The last statement end. ends your program.
CompileandExecutePascalProgram
 Open a text editor and add the above-mentioned code.
 Save the file as hello.pas
 Open a command prompt and go to the directory, where you saved the file.
 Type fpc hello.pas at command prompt and press enter to compile your code.
 If there are no errors in your code, the command prompt will take you to the
next line and would generate hello executable file and hello.o object file.
 Now, type hello at command prompt to execute your program.
 You will be able to see "Hello World" printed on the screen and program waits
till you press any key.
$ fpc hello.pas
Free Pascal Compiler version 2.6.0 [2011/12/23] for x86_64
Copyright (c) 1993-2011 by Florian Klaempfl and others

Pascal
14
Target OS: Linux for x86-64
Compiling hello.pas
Linking hello
8 lines compiled, 0.1 sec
$ ./hello
Hello, World!
Make sure that free pascal compiler fpc is in your path and that you are running it in
the directory containing source file hello.pas.

Pascal
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You have seen a basic structure of pascal program, so it will be easy to understand
other basic building blocks of the pascal programming language.
Variable
A variable definition is put in a block beginning with a var keyword, followed by
definitions of the variables as follows:
var
A_Variable, B_Variable ... : Variable_Type;
Pascal variables are declared outside the code-body of the function which means they
are not declared within the begin and end pairs, but they are declared after the
definition of the procedure/function and before the begin keyword. For global
variables, they are defined after the program header.
Functions/Procedures
In Pascal, a procedure is set of instructions to be executed, with no return value
and a function is a procedure with a return value. The definition of
function/procedures will be as follows:
Function Func_Name(params...) : Return_Value;
Procedure Proc_Name(params...);
Comments
The multiline comments are enclosed within curly brackets and asterisks as {* ... *}.
Pascal allows single-line comment enclosed within curly brackets { ... }.
{* This is a multi-line comments
and it will span multiple lines. *}
{ This is a single line comment in pascal }
4. BASIC SYNTAX

Pascal
16
CaseSensitivity
Pascal is a case non-sensitive language, which means you can write your variables,
functions, and procedure in either case. Like variables A_Variable, a_variable and
A_VARIABLE have same meaning in Pascal.
PascalStatements
Pascal programs are made of statements. Each statement specifies a definite job of
the program. These jobs could be declaration, assignment, reading data, writing data,
taking logical decisions, transferring program flow control, etc.
For example:
readln (a, b, c);
s := (a + b + c)/2.0;
area := sqrt(s * (s - a)*(s-b)*(s-c));
writeln(area);
ReservedWordsinPascal
The statements in Pascal are designed with some specific Pascal words, which are
called the reserved words. For example, the words, program, input, output, var, real,
begin, readline, writeline and end are all reserved words. Following is a list of
reserved words available in Pascal.
and array begin case const
div do downto else end
file for function goto if
in label mod nil not
of or packed procedure program
record repeat set then to
type until var while with

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CharacterSetandIdentifiersinPascal
The Pascal character set consists of:
 All upper case letters (A-Z)
 All lower case letters (a-z)
 All digits (0-9)
 Special symbols - + * / := , . ;. () [] = {} ` white space
The entities in a Pascal program like variables and constants, types, functions,
procedures and records, etc., have a name or identifier. An identifier is a sequence
of letters and digits, beginning with a letter. Special symbols and blanks must not be
used in an identifier.

Pascal
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Data types of an entity indicates the meaning, constraints, possible values,
operations, functions and mode of storage associated with it. Integer, real, boolean
and character types are referred as standard data types. They can be categorized as
scalar, pointer and structured data types. Examples of scalar data types are integer,
real, boolean, character, subrange and enumerated. Structured data types are made
of the scalar types; for example, arrays, records, files and sets. We will discuss the
pointer data types later.
PascalDataTypes
Pascal data types can be summarized as below in the following diagram:
5. DATA TYPES

Pascal
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TypeDeclarations
The type declaration is used to declare the data type of an identifier. Syntax of type
declaration is:
type-identifier-1, type-identfier-2 = type-specifier;
For example, the following declaration defines the variables days and age as integer
type, yes and true as boolean type, name and city as string type, fees and expenses
as real type.
type
days, age = integer;
yes, true = boolean;
name, city = string;
fees, expenses = real;
IntegerTypes
Following table gives you details about standard integer types with its storage sizes
and value ranges used in Object Pascal:
Type Minimum Maximum Format
Integer -2147483648 2147483647 signed 32-bit
Cardinal 0 4294967295 unsigned 32-bit
Shortint -128 127 signed 8-bit
Smallint -32768 32767 signed 16-bit
Longint -2147483648 2147483647 signed 32-bit
Int64 -2^63 2^63 - 1 signed 64-bit
Byte 0 255 unsigned 8-bit
Word 0 65535 unsigned 16-bit

Pascal
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Longword 0 4294967295 unsigned 32-bit
Constants
Use of constants makes a program more readable and helps to keep special quantities
at one place in the beginning of the program. Pascal allows numerical, logical,
string and character constants. Constants can be declared in the declaration part of
the program by specifying the const declaration.
Syntax of constant type declaration is as follows:
const
Identifier = contant_value;
Following are some examples of constant declarations:
VELOCITY_LIGHT = 3.0E=10;
PIE = 3.141592;
NAME = 'Stuart Little';
CHOICE = yes;
OPERATOR = '+';
All constant declarations must be given before the variable declaration.
Enumeratedtypes
Enumerated data types are user-defined data types. They allow values to be specified
in a list. Only assignment operators and relational operators are permitted on
enumerated data type. Enumerated data types can be declared as follows:
type
enum-identifier = (item1, item2, item3, ... )
Following are some examples of enumerated type declarations:
type
SUMMER = (April, May, June, July, September);
COLORS = (Red, Green, Blue, Yellow, Magenta, Cyan, Black, White);
TRANSPORT = (Bus, Train, Airplane, Ship);

Pascal
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The order in which the items are listed in the domain of an enumerated type defines
the order of the items. For example, in the enumerated type SUMMER, April comes
before May, May comes before June, and so on. The domain of enumerated type
identifiers cannot consist of numeric or character constants.
SubrangeTypes
Subrange types allow a variable to assume values that lie within a certain range. For
example, if the age of voters should lie between 18 to 100 years, a variable named
age could be declared as:
var
age: 18 ... 100;
We will look at variable declaration in detail in the next section. You can also define
a subrange type using the type declaration. Syntax for declaring a subrange type is
as follows:
type
subrange-identifier = lower-limit ... upper-limit;
Following are some examples of subrange type declarations:
const
P = 18;
Q = 90;
type
Number = 1 ... 100;
Value = P ... Q;
Subrange types can be created from a subset of an already defined enumerated type,
For example:
type
months = (Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec);
Summer = Apr ... Aug;
Winter = Oct ... Dec;

Pascal
22
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 applied 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:
BasicVariablesinPascal
Type Description
Character Typically a single octet (one byte). This is an integer type.
Integer The most natural size of integer for the machine.
Real A single-precision floating point value.
Boolean
Specifies true or false logical values. This is also an
integer type.
Enumerated Specifies a user-defined list.
Subrange Represents variables, whose values lie within a range.
String Stores an array of characters.
Pascal programming language also allows defining various other types of variables,
which we will cover in subsequent chapters like Pointer, Array, Records, Sets, and
Files, etc. For this chapter, let us study only basic variable types.
6. VARIABLE TYPES

Pascal
23
VariableDeclarationinPascal
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 list of
variables, followed by a colon (:) and the type. Syntax of variable declaration is:
var
variable_list : type;
Here, type must be a valid Pascal data type including character, integer, real,
boolean, or any user-defined data type, etc., and variable_list may consist of one or
more identifier names separated by commas. Some valid 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, holidays : days;
choice: yes;
student_name, emp_name : name;
capital: city;

Pascal
24
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.
VariableInitializationinPascal
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 initialized with zero. They may contain rubbish
values. So it is a better practice to initialize variables in a program. Variables can be
initialized (assigned an initial value) in their declaration. The initialization is followed
by the var keyword and the syntax of initialization 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

Pascal
25
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.
When the above code is compiled and executed, it produces the following result:
Please enter your first name:
John
Please enter your surname:
Smith
Welcome to the world of Pascal John Smith
EnumeratedVariables
You have seen how to use simple variable types like integer, real and boolean. Now,
let's see variables of enumerated type, which can be defined as:
var
var1, var2, ... : enum-identifier;
When you have declared an enumerated type, you can declare variables of that type.
For example,
type
months = (January, February, March, April, May, June, July, August,
September, October, November, December);
Var
m: months;
...
M := January;

Pascal
26
The following example illustrates the concept:
program exEnumeration;
type
beverage = (coffee, tea, milk, water, coke, limejuice);
var
drink:beverage;
begin
writeln('Which drink do you want?');
drink := limejuice;
writeln('You can drink ', drink);
end.
Which drink do you want?
You can drink limejuice
SubrangeVariables
Subrange variables are declared as:
var
subrange-name : lowerlim ... uperlim;
Examples of subrange variables are:
var
marks: 1 ... 100;
grade: 'A' ... 'E';
age: 1 ... 25;
The following program illustrates the concept:
program exSubrange;
var
marks: 1 .. 100;

Pascal
27
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

Pascal
28
A constant is an entity that remains unchanged during program execution. Pascal
allows only constants of the following types to be declared:
 Ordinal types
 Set types
 Pointer types (but the only allowed value is Nil).
 Real types
 Char
 String
DeclaringConstants
Syntax for declaring constants is as follows:
const
identifier = constant_value;
The following table provides examples of some valid constant declarations:
Constant Type Examples
Ordinal(Integer)type
constant
valid_age = 21;
Set type constant Vowels = set of (A,E,I,O,U);
Pointer type constant P = NIL;
Real type constant e = 2.7182818; velocity_light = 3.0E+10;
Character type constant Operator = '+';
7. CONSTANTS

Pascal
29
String type constant president = 'Johnny Depp';
The following example illustrates the concept:
program const_circle (input,output);
const
PI = 3.141592654;
var
r, d, c : real; {variable declaration: radius, dia, circumference}
begin
writeln('Enter the radius of the circle');
readln(r);
d := 2 * r;
c := PI * d;
writeln('The circumference of the circle is ',c:7:2);
end.
Enter the radius of the circle
23
The circumference of the circle is 144.51
Observe the formatting in the output statement of the program. The variable c is to
be formatted with total number of digits 7 and 2 digits after the decimal sign.

Pascal
30
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