A/L 2011 revision. PASCAL PROGRAMMING fileA/L 2011_revision. PASCAL PROGRAMMING page 1 of 8 Pascal is a high level programming language developed by Niklaus Wirth in 1970 based on

A/L 2011_revision. PASCAL PROGRAMMING

page 1 of 8

Pascal is a high level programming language developed by Niklaus Wirth in 1970 based on the ALGOL programming language. It was named in honor of the French mathematician and philosopher Blaise Pascal. Pascal programs saved as *.pas.

Variables store values/data

Constants stay the same

Control Flow change directions

Procedures sub routines

Functions sub routines returning a value

Comments notes

Structure of a Pascal program

PROGRAM ProgramName (FileList);uses crt; (*importing libraries)

const (* Constant declarations *)type

(* Type declarations *)var

(* Variable declarations *)(* Subprogram definitions *)begin (* Main Program statements *)end.

program FirstProg;

begin

Writeln('Hello World!');

end.


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VARIABLES

Must begin with a letter

Can include alphanumeric characters and underscore (_).

May not contain ~ ! @ # $ % ^ & * ( ) + ` - = { } [ ] : " ; ' < > ? , . / |

CONSTANTS

Value assigned to a constant at the beginning of the program. It can’t be changed during the program running.

Const Pi = 3.1415926535897932; Gravity = 9.8; GoldenRatio = 1.6; a : real = 12;


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VARIABLES AND DATA TYPES

Var IdentifierList1 : DataType1; IdentifierList2 : DataType2; IdentifierList3 : DataType3;

The basic data types

integer From -32768 to 32767

real () 3.4x10-38 to 3.4x1038

Char “A”

string “Niranjan”

Boolean TRUE and FALSE

var IndexNumber, Age: integer Temperature :real; FirstName: string; Married: Boolean

ASSIGNMENT AND OPERATIONS

variable_name := expression;

length := 385.38;

totalarea := (37.57 * 5.93) + (38.2/2.1);


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OPERATORS

+ Addition- Subtraction* Multiplication/ Divisiondiv Integer divisionmod Modulus (remainder division)

PUNCTUATION AND INDENTATION

Pascal ignores end-of-lines and spaces.punctuation (;) tells the compiler when a statement ends.

program Compute; const a = 5; b = 385.3;

var alpha, beta : real;

begin (* main *) alpha := a + b; beta := b / aend. (* main *)

COMMENTS

(* one line *)(* some comments go into several lines*)


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INPUT / OUTPUT

read (Variable_List); readln (Variable_List);

read (a); readln (b);read (a, b, c, d); readln (e, f);

write (Argument_List);writeln (Argument_List);

write (a);writeln (b,c,d);write ('Time:', time:2);

program InputOutput;

vara, b : string;begin (* main *) read(a); readln(b); writeln(a) writeln(a)end.


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CONDITIONALS RELATIONAL OPERATORS:

<>=

<=>=<>

less than greater than

equal to less than or equal to

greater than or equal to not equal to

5 < 72 > 14=3+12<=310>=5“A” <>”B”

IF … THEN

if BooleanExpression then

Statement1;

if A = 30 then Writeln('A is equal to 30');

IF … THEN …. ELSE

if BooleanExpression then StatementIfTrue

else

StatementIfFalse;

if A = 30 then

Writeln('A is equal to 30')

else

Writeln('A is not equal to 30');


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NESTED IF

if Condition1 then

Statement1

else

if Condition2 then

Statement2

else

Statement3;

if A=30 then

Writeln('A is equal to 30');

else

if A=50 then

Writeln('A is equal to 50');

else

Writeln('A is not 30 or 50');

CASE

case selector of

List1: Statement1;

List2: Statement2;

...

Listn: Statementn;

otherwise Statement

end;

Choice := ReadKey;

case Choice of 'a': Writeln('You like apples'); 'b': Writeln('You like bananas'); 'c': Writeln('You like carrots');else Writeln('Your choice is not a, b or c');


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LOOPINGFOR NEXT

for index := Low to High do statements;

sum := 0;

for count := 1 to 100 do sum := sum + count;

WHILE .. DO

while BooleanExpression do

begin statements;

end.

a := 5;

while a < 6 do

writeln (a);

a := a + 1

REPEAT … UNTIL

repeat statement1;

until BooleanExpression;

a := 5;

repeat a := a + 1; writeln (a);until a > 10

GOTO

LABEL 10; statements;

GOTO 10;


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BREAK and CONTINUE

The Break command will exit a loop at any time.

program breakTest; var i: Integer;begin i := 0; repeat i := i + 1; break; Writeln(i);until i = 10;end.

program breakTest; var i: Integer;begin i := 0; repeat i := i + 1; continue; Writeln(i);until i = 10;end.

Program 1 will not print anything because break it exits the loop before it gets there.

In Program 2 continuecommand will jump back to the top of a loop

ARRAYS

var

X: ARRAY [1..5] of real;begin

X[1]:=4.2; X[2]:=71.6; X[3]:=8.3; X[4]:=92.6; X[5]:=403.7; writeln (X[1]+X[2]+X[3]+X[4]+X[5])

end.


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PROCEDURES & FUNCTIONSProcedure has the same basic format as a program:

procedure Name;

const (* Constants *)

Var(* Variables *)

Begin (* Statements *)end;

Parameters to the procedure passed in the heading

procedure PrintParameters (a, b : integer; c, d : real);

begin a := 10; b := 2; writeln (a, b, c, d)end;

FUNCTIONS

function functionName (parameter_list) : return_type; statements;

function add1toParameter(a) : integer;begin add1toParameter:= a + 1end.

BUILT IN FUNCTIONS

abs returns absolute valuearctan returns arctan in radianscos returns cosine of a radian measuresin returns sin of a radian measuresqr returns square (power 2) sqrt returns root (power 1/2)chr character with given ASCII value round returns round to nearest integer


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MATH FUNTIONSABS(-6) the absolute value of -6; gives 6SQR(3) the square of 3; gives 9SQRT(9) the square root of 9; gives 3.0SIN(2) the sine of 2 radians measureCOS(2) the cosine of 2 radians measureLN(9) the natural logarithm of 9; gives loge 9ROUND(9.2) rounds a number; gives 9

Functions are used to do repetitive tasks to reduce repeating code.

program AddEmUpAgain;

function AddEmUp( a, b, c: integer ) : integer;

begin AddEmUp := a + b + c; end;

procedure PrintData( a, b, c: integer );

begin Writeln('The sum of a, b, and c is ', AddEmUp(a, b, c), '.'); end;

begin

PrintData(2, 3, 4);

end.


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SAMPLE PROGRAMS

Find the sum and average of five numbers

program SumAverage;

const

NumberOfIntegers = 5;

var

A, B, C, D, E : integer; Sum : integer; Average : real;

begin (* Main *)

A := 45; B := 7; C := 68; D := 2; E := 34; Sum := A + B + C + D + E;

Average := Sum / NumberOfIntegers; writeln ('Number of integers = ', NumberOfIntegers); writeln ('Number1 = ', A); writeln ('Number2 = ', B); writeln ('Number3 = ', C); writeln ('Number4 = ', D); writeln ('Number5 = ', E); writeln ('Sum = ', Sum); writeln ('Average = ', Average)

end. (* Main *)


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Input 5 numbers and print their sum and average

program SumAverage;

const

NumberOfIntegers = 5;

var

A, B, C, D, E : integer; Sum : integer; Average : real;

begin (* Main *)

write ('Enter the first number: '); readln (A); write ('Enter the second number: '); readln (B); write ('Enter the third number: '); readln (C); write ('Enter the fourth number: '); readln (D); write ('Enter the fifth number: '); readln (E);

Sum := A + B + C + D + E;

Average := Sum / 5; writeln ('Number of integers = ', NumberOfIntegers); writeln; writeln ('Number1:', A:8); writeln ('Number2:', B:8); writeln ('Number3:', C:8); writeln ('Number4:', D:8); writeln ('Number5:', E:8); writeln ('================'); writeln ('Sum:', Sum:12); writeln ('Average:', Average:10:1);

end.


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SCOPEWhere will the variables be visible?

program ScopeDemo;var A, B : integer;

procedure ScopeInner; begin B:= 10; writeln (B); (* prints value 10 *) writeln (A); (* prints value 20 *)end;

begin (* Main *) A := 20; writeln (A); (* prints value 20 *) ScopeInner; (*changes A value*) writeln (A); (* prints new value 10*)end. (* Main *)

global variables A visible everywhereglobal variables can be changed inside procedures.


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RCURSIONRecursion allows a function or procedure to call itself

function Sum (num : integer) : integer;begin if num = 1 then Sum := 1else Sum := Sum(num-1) + num;(* calls self again*)end;

begin totalsum:=Sum(10); writeln(totalsum);end.

If we call Sum with 3 as parameter

totalsum := Sum(3);

1st call : Sum(3) becomes Sum(2) + 3.

2nd call : Sum(2) becomes Sum(1) + 2.

At 1, the recursion stops and becomes 1 and returns

Sum(2) becomes 1 + 2 = 3.

Sum(3) becomes 3 + 3 = 6.

a becomes 6.


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FORWARD REFERENCING

procedures/functions can only use variables and subprograms already defined before them. (this is a weakness in Pascal coding)

procedure Second (parameter list); procedure First (parameter list);procedure Third (parameter list);

procedure First;begin Second (parameter list);(*Second is declared before First *)end;

procedure Second;begin Third (parameter list); (* ERROR Third is not visible to Second*)end;


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Find the first 100 numbers in the Fibonacci sequence. 1 1 2 3 5 8 13 21 …..

program Fibonacci;

var

Fibonacci1, Fibonacci2 : integer; temp : integer; count : integer;

begin (* Main *)writeln ('First ten Fibonacci numbers are:');count := 0;Fibonacci1 := 0;Fibonacci2 := 1;

repeat write (Fibonacci2:7); temp := Fibonacci2; Fibonacci2 := Fibonacci1 + Fibonacci2; Fibonacci1 := Temp; count := count + 1until count = 10;

writeln;

(*you can also use a FOR loop or a WHILE loop. *)

end. (* Main *)

ASSIGNMENT

Modify above program to display all powers of 2 up to 200.What code would you change and why?


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FILE HANDLINGReading and Writing to Files

read (file_variable, argument_list);write (file_variable, argument_list); rest (file_variable, 'filename' ) rewrite (file_variable, 'filename'); assign (file_variable, 'filename');eoln (file_variable) eof (file_variable)

Reads values from a fileWrite values to a fileOpens a file for reading Opens a file for writingAssigns a filename to a variableReturns TRUE when end of line is reachedReturns TRUE when end of file is reached

program CopyOneByteFile;

var mychar : char; filein, fileout : text;

begin assign (filein, 'c:\file1.txt'); reset (filein); assign (fileout, 'c:\file2.txt'); rewrite (fileout); read (filein, mychar); write (fileout, mychar); close(filein); close(fileout)end.


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BOOLEAN EXPRESSIONS

not and or xor

negation conjunction disjunctionexclusive-or

(~) (^) (v)

NOT applied to only one value to invert it:

NOT true = false NOT false = true

AND gives TRUE only if both values are TRUE:

TRUE and FALSE = FALSE TRUE and TRUE = TRUE

OR yields TRUE if at least one value is TRUE:

TRUE or TRUE = TRUE TRUE or FALSE = TRUE FALSE or TRUE = TRUE FALSE or FALSE = FALSE

XOR yields TRUE if one expression is TRUE and the other is FALSE.

TRUE xor TRUE = FALSE TRUE xor FALSE = TRUE FALSE xor TRUE = TRUE FALSE xor FALSE = FALSE


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Bubble sort moves the biggest numbers to the end of the array.Example of Sorting 5 Numbers

program BubbleSort;

var

a: array[1..5] of Integer;

i, j, tmp: Integer;

begin

a[1] := 23; a[2] := 45; a[3] := 12; a[4] := 56; a[5] := 34;

for i := 1 to 4 do

for j := i + 1 to 5 do

if a[i] > a[j] then

begin

tmp := a[i]; a[i] := a[j]; a[j] := tmp; end;

for i := 1 to 5 do

writeln(i,': ',a[i]);

end.


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Programming Solution: the Towers of Hanoi Problem

program TowersofHanoi;

var numdiscs : integer;

procedure DoTowers (NumDiscs, OrigPeg, NewPeg, TempPeg : integer);(* Explanation of variables Number of discs -- number of discs on OrigPeg OrigPeg -- peg number of the tower NewPeg -- peg number to move the tower to TempPeg -- peg to use for temporary storage*)

begin (* Take care of the base case -- one disc *)

if NumDiscs = 1 then writeln (OrigPeg, ' ---> ', NewPeg) (* Take care of all other cases *)else begin (* First, move all discs except the bottom disc to TempPeg, using NewPeg as the temporary peg for this transfer *)

DoTowers (NumDiscs-1, OrigPeg, TempPeg, NewPeg);

(* Now, move the bottom most disc from OrigPeg to NewPeg *)

writeln (OrigPeg, ' ---> ', NewPeg);

(* Finally, move the discs currently on TempPeg to NewPeg, use OrigPeg as the temporary peg for this transfer *)

DoTowers (NumDiscs-1, TempPeg, NewPeg, OrigPeg) endend;

begin (* Main *) write ('Please enter the number of discs in the tower ===> ') readln (numdiscs); writeln; DoTowers (numdiscs, 1, 3, 2)end. (* Main *)

Tower of Hanoi is a problem with three pegs and more than 3 disks on one peg.

You have to move disks one by one from peg to peg to transfer all disks to one peg.

Rules1. Only one disk can be transferred at a time.

2. Smaller disk should always be on the top of the other.


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program Decisions;

var i: Integer;

begin Writeln('Enter a number'); Readln(i); if i > 5 then Writeln('Greater than 5');end.

program Decisions;

var i: Integer;

begin Writeln('Enter a number'); Readln(i); if i > 5 then Writeln('Greater than 5') else Writeln('Not greater than 5');end.

program Loops1;

var i: Integer;

begin i := 0; while i <= 10 begin i := i + 1; Writeln('Hello'); end;end.

program Loops2;

var i: Integer;

begin i := 0; repeat i := i + 1; Writeln('Hello'); until i = 10;end.

Download FREE Pascal

http://www.freepascal.org

Created by: Niranjan Meegammana, Shilpa Sayura Project. Supported by YES & ICT @ OSIPTO, KANDY.www.shilpasayura.org

A/L 2011 revision. PASCAL PROGRAMMING fileA/L 2011_revision. PASCAL PROGRAMMING page 1 of 8 Pascal is a high level programming language developed by Niklaus Wirth in 1970 based on

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