ICT For All Classes : Pascal Programming for Beginners

Pascal Programming

Pascal is high level and general purpose programming language. It has several advantages such as easy to learn, structured language, can create efficient program. It is platform independent can compiled variety of platforms. It is a non. case sensitive language

Pascal Program Structure

A Pascal program has the following parts. It is not compulsory to have all parts in a program.
{ } is used to have comments where ever needed to improve maintainability. compiler ignore the comments.

program test; {name of the program}
uses crt; {libraries to use}
const  {declare global constant }
	pi=22/7;

var {declare global variable}
	x: integer;

function {Declare functions}
{ local variables }
begin
...
end;

procedure {declare procedures}
var{ local variables }
begin
...
end;

begin { main program}
...
end. {end of main}

Keywords

Following are the 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

Pascal identifiers

Pascal program has several entities such as variables, constants, types, functions, procedures, records, etc. The entities have a name called identifier.

Pascal identifiers
* Start with alphabet
* Without Spaces
* Underscore not as first letter
* Special characters are not allowed (&, $, %, *, = , + ...)

Correct identifiers	Wrong identifiers
ABC, Abx, A_123, Tot_Price	123, 1ABC, abc xyz, _123, tot&

Pascal Program to Display Messages

The below programs display the messages in the screen. The command to display the messages in the screen is writeln or write.

program FirstPascal ;

begin
	writeln('My first Program');
	writeln('Pascal');
	readln;
end.

Output
My first Program
Pascal


Program second;
begin
	write('10+20=');
	writeln(10+20);
	readln;
end.

Output
10+20=30

Variables in Pascal

A variable is a name given to a storage area that a program accesses to manipulate. Each variable has a specific type and each type has its own size which is allocated in the Memory.

Data types in Pascal	Literals
integer	10,20.50,150
char	'A','B','C'
real	5.60, 150.75
string	'Pascal'
boolean	true, false

program PasVariables;
var
	num1: integer;
	num2:integer;
begin
	num1:=15;
	num2:=20;
	write('num1+num2=');
	writeln(num1+num2);
        readln;
end.

Output
num1+num2=35

User Input

Pascal command read/readln is used to get input form the user.

program UserDatain;
var
	num1: integer;
	num2:integer;
begin
	write('Enter a number?');
	readln(num1);
	write('Enter another number?');
	readln(num2);
	write('num1+num2=');
	writeln(num1+num2);
	readln;
end.

Output
Enter a number?150
Enter another number?200
num1+num2=350

Arithmetic operators in Pascal

Arithmetic operator	Description
+	Addition
-	Subtraction
/	Division
*	Multiplication
mod	Remainder
div	Whole integer when divide

program PascalArithmetic;
var
	num1: integer;
	num2:integer;
begin
	write('Enter a number?');
	readln(num1);
	write('Enter another number?');
	readln(num2);
	writeln('Addition=' , num1+num2);
	writeln('Deduction=' , num1-num2);
	writeln('Multiplication=' , num1*num2);
	writeln('Division=' , num1/num2:10:2);
	writeln('Mod=' , num1 mod num2);
	writeln('Div=' , num1 div num2);
	readln;
end.

Output
Enter a number?100
Enter another number?6
Addition=106
Deduction=94
Multiplication=600
Division=     16.67
Mod=4
Div=16

Relational Operators

Relational Operators are used to compare two values and evaluate it. The final result is true or false.

Logical Operator	Description
>=	Greater than or Equal
>=	Greater than or Equal
<	Less Than
<=	Less than or Equal
<>	Not Equal

program PasRelationalOp;
var
	num1:integer;
	num2:integer;
begin
	write('Enter a number?');
	readln(num1);
	write('Enter another number?');
	readln(num2);
	writeln(num1,' > ',num2 , num1>num2);
	writeln(num1,'>=',num2 , num1>=num2);
	writeln(num1,'=',num2 , num1=num2);
	writeln(num1,' <>',num2 , num1 <>num2);
	writeln(num1,'<',num2 , num1 < num2);
	writeln(num1,'<=',num2 , num1 <= num2);
	readln;

end. 

Output
Enter a number?10
Enter another number?2
10  > 2TRUE
10 >=2TRUE
10=2FALSE
10 <>2TRUE
10 <2FALSE
10 <=2FALSE

Logical Operators

Logical Operator
not
and
or

program PasLogicalOp;
var
	num1:integer;
	num2:integer;
begin
	write('Enter a number?');
	readln(num1);
	write('Enter another number?');
	readln(num2);
	writeln('> ' , (num1>50) and (num2>50));
	writeln('>= ' , (num1>50) or (num2>50));
	writeln('= ' , not (num1>50) );
	readln;

end.


Output
Enter a number?10
Enter another number?5
> FALSE
>= FALSE
= TRUE

Control Structure in Pascal

There are three types of control structure in any programming. They are

Sequence
Selection
Repetition

Selection Control Structure (If .... then ..... else)

program PasSelection;
var
	num1:integer;
	num2:integer;
begin
	write('Enter a number?');
	readln(num1);
	write('Enter another number?');
	readln(num2);
	if num1>num2 then
		writeln('Number 1 > number 2')
	else
		write('Number 1 <= number 2');
	readln;
end.    


Output
Enter a number?100
Enter another number?150
Number 1 <= number 2



program PasSelOddEven;
var
	x:integer;
begin
	write('Enter a number?');
	readln(x);
	if x mod 2 = 1 then
		writeln('the number is odd....')
	else
		writeln('The nuber is even...');
	readln;

end.


Output
Enter a number?11
the number is odd....



program mark;{nested if}
var
	m:integer;
	g:char;
begin
	write('Enter your marks');
	readln(m);
	if m>=75 then
		g:='A'
	else
		if m >65 	then
			g:='B'
		else
			if m >=50 then
				g:='C'
			else
				if mgt;=35 then
					g:='S'
				else
					g:='F' ;
	writeln('your Marks is ',m);
	writeln('Your Grade is ',g);
        readln();
end.


Output
Enter your marks69
your Marks is 69
Your Grade is B

Selection Control Struture (case ... of)

program PasCase;
var
	g:char;
begin
	write('Enter your grade(A,B,C,S,F) ?');
	readln(g);
	case g of
		'A' : writeln('Excellent');
		'B' : writeln('Good');
		'C' : writeln('Great');
		'S' : writeln('Bad');
		'F' : writeln('Very Bad');
	end;
	readln;
end.



Output
Enter your grade(A,B,C,S,F) ?B
Good

Control Structure Repetition/Loop/Iteration

Repetition (While)

program PasWhile;
var
	x:integer;
begin
	x:=1;
	while xlt;=10 do
	begin
		writeln(x);
		x:=x+1;
	end;
	readln;
end.
 
Output
1
2
3
4
5
6
7
8
9
10

Repetition (for)

program PasFor;
var
	x:integer;
begin
	for x:=1 to 10 do
		writeln(x);
	readln;
end. 


Output
1
2
3
4
5
6
7
8
9
10



program PasFor;
var
	x:integer;
begin
	for x:=10 downto 1 do
		writeln(x);
	readln;
end.  

Output
10
9
8
7
6
5
4
3
2
1

Repetition (repeat ... until)

program PasRepeatUntil;
var
        x:integer;
begin

	x:=1;
	repeat
		writeln(x);
		x:=x+1;
	until x >10;
	readln
end. 


Output
1
2
3
4
5
6
7
8
9
10

Subroutine in Pascal

The subroutine perform a specific task which need to be done more than once at various points in the main program.

Advantage of subroutine

* Easy to Test
* Easy to maintain
* Reuse
* Less lines of code
* Task can be shared

Procedure in Pascal without Parameter

program PasSub;

procedure star();
begin
	writeln('*****');
end;

procedure dash();
begin
	writeln('-----');
end;

begin
	star();
	dash();
	star();
	dash();
	dash();
        readln;
end.     


Output
*****
-----
*****
-----
-----

Procedure in Pascal with Parameter

procedure Mypat(x:char; y:integer);
var
	i:integer;
begin
	for i:=1 to y do
	begin
		write(x);
	end;
        writeln();
end;

begin
	mypat('=',10);
	mypat('-',20);
	mypat('$',30);
	readln;
end.


Output
==========
--------------------
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

Functions in Pascal

function AreaCircle(r:real):real;
const
	pi=22/7;
begin
	AreaCircle:=pi*sqr(r);
end;

begin;
        writeln(AreaCircle(10):8:2);
        writeln(AreaCircle(30):8:2);
	writeln(AreaCircle(100):8:2);

	readln();
end. 


Output
  314.29
 2828.57
31428.57

Array

An array is a data structure which stores elements of the same data type in a contiguous memory location with a name (array name). Its elements are accessed by using the index with the array name.

Arrays in Pascal

program PasArr;
const
  L=2 ;
var
  name: array[0..L]of string;
  marks1: array[0..L]of integer;
  marks2: array[0..L]of integer;
  i:integer;

begin
  for i:=0 to L do
  begin
    writeln('Enter name,maths,science?');
    readln(name[i]);
    readln(marks1[i]);
    readln(marks2[i]);
  end;
  writeln();
  Writeln('Marks and Names are');
  for i:=0 to L do
  begin
    write(name[i],' - ');
    write(marks1[i],' - ');
    write(marks2[i]);
    writeln;
  end;
  readln;
end.
     

Output
Enter name,maths,science?
Ganesh
90
88
Enter name,maths,science?
Peter
100
90

Marks and Names are
Ganesh - 90 - 88
Peter - 100 - 90

Note for Programmer

When you write program, follow certain disciplines. It will help to keep program maintainability. Some of them are:

* Use meaningful variables and identifier names
* Use indentation
* Where ever Possible comment
* Avoid goto statement
* Limit Lines of Code (use modular approach)

ICT For All Classes

Pascal Programming for Beginners