1 st semester 2004 1 basic pascal elements อภิรักษ์...

11st semester 2004

Basic Pascal Elements

อภิ�รั�กษ์� จั�นทรั�สรั�างAphirak Jansang

aphirak.j@ku.ac.thhttp://www.cpe.ku.ac.th/~aphirak

Computer Engineering DepartmentKasetsart University, Bangkok THAILAND

21st semester 2004

Outlines

Pascal Program Structure Constant/Variable STATEMENT EXPRESSION

31st semester 2004

Identifiers – AGAIN FROM Lecture1

Symbolic names for program elements

Rules for constructing identifiers Letters, digits, and under score (_) First character letter Can be long (63 char) Reserved words are not allowed

41st semester 2004

Pascal PROGRAM STRUCTUREprogram myFirstProgram;const

myStudentId = 1234567;var

courseTaken: integer;begin

write(‘Please Enter a number of courses’);read(‘courseTaken’);writeln(‘Student’, myStudentId, ‘ takes ’, courseTaken, ‘ courses in this semester’);

end.

Program Heading

Declarations

Program Body

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Pascal PROGRAM STRUCTURE

PROGRAM HEADING

DECLARATIONS

NONAME00.PASNONAME00.PAS

PROGRAM BODY

PROGRAM HEADING

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PROGRAM HEADING

Place at the beginning of file Parameter

input - keyboard output - monitor

Heading Syntax program YOURPROGNAME (input,

output); program YOURPROGNAME ;

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PROGRAM HEADING Example Valid PROGRAM Heading

program calulate_grade (input, output); program square_root (input, output); program lab3;

Invalid PROGRAM Heading program registration (input, output) program polynomial (input, ); program calculate-area (input, output);

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Pascal PROGRAM STRUCTURE

NONAME00.PASNONAME00.PAS

PROGRAM HEADING

DECLARATIONS

PROGRAM BODY

PROGRAM HEADING

DECLARATIONS

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Declarations

1. CONSTANT 2. VARIABLE

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CONSTANT

Value cannot be changed Syntax

Constidentifier1 = constant expression 1;………indentifier_n = constant expression n;

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Constant Declaration Example

ConstMyLargeInteger = 9999; {value is 9999}

MySmallInteger = -MyLargeInteger; {value is -9999}

Star = ‘*’; {value is symbol *}

FirstMonth = ‘January’; {value is string ‘January’}

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VARIABLE

Referred to an individual cell in main memory

Value can be changed Syntax

VARidentifier1 : data type;

identifier3, identifier2 : data type;

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VARIABLE Declaration Example

VarX, Y : Real;AREA: Real;

AREAAREA

YY

XX

NONAME00.PASNONAME00.PAS

MAIN MEMORY

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VARIABLE Data type

CHAR INTEGER REAL BOOLEAN

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CHAR data type A single character

Letter Digit Symbol

Character value in program must be enclosed with single quote EX. ‘gg’ ‘AA’ ‘11’ ‘**’

A sequence of character is known as STRING EX. ‘Harry PotterHarry Potter’, ‘Protocol SystemProtocol System’

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Example CHAR data type Declaration

Varch1 : char;st1 : string;

ch1ch1

st1st1

MAX=255MAX=255

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INTEGER data type

Value can be positive or negative number In i386, integer variable can keep value

from -32768 to 32767

Bigger than integer is longint data type-2147483648 to 2147483647

Can be used with arithmetic operation

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Example Integer data type Declaration

Varnum1 : integer;num2, num3 : integer

;num4 : longint;num6, num7 :

longint;

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REAL data type Integer + Fraction

Example

999999 888888..

Integer Fraction

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REAL Data type

Can be used in following notation Decimal notation Example 2.50, 99.99 Scientific notation

number x 10exponent

Are expressed in Pascal using the syntax

<number> E <exponent>

Example 2.5E+00, 9.999+E1

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Real data type

Can be used with +, -, *, / and comparison

Example .2345 Invalid 1,250.00 Invalid -1250.00 Valid 50E10 Valid

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BOOLEAN data type

Value can be TRUETRUE or FALSEFALSE Use Frequently in Control Statement Example

Variable A is the boolean data type.We can use following

A := 11>211>2; True

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CONCLUSION FROM PREVIOUS

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Pascal PROGRAM STRUCTURE

NONAME00.PASNONAME00.PAS

PROGRAM HEADING

DECLARATIONS

PROGRAM BODY

PROGRAM HEADING

DECLARATIONS

PROGRAM BODY

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PROGRAM BODY

BeginBeginstatement1;statement2;…statementn;

End.End.

PROGRAM BODYPROGRAM BODY

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EXPRESSION

ARITHMETIC EXPRESSION BOOLEAN EXPRESSION

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Arithmetic Expression Operators:

+ - * / DIV (truncated divide) MOD (remainder after division)

Example 11/2 = 5.5 11 DIV 2 = 5 11 MOD 2 = 1

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Arithmetic Expression

45.00 (width + length) (12*(top – bottom)) 34+54/78*12

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Precedence rules for arithmetic operators

1. ( ) parentheses2. Unary + and –3. *, / , DIV , MOD4. + –5. If equal precedence, left to rightExamples-a+j/-w = (-a) + (j / (-w))

C*23/6+23mod2 = ((C*23)/6) + (23 mod 2)

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Precedence rules for arithmetic operators

Examples

C

BAX

X:=A+B/C;

WRONG

X:=A+(B/C);

X:=(A+B)/C;TRUETRUE

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Boolean Expression Two possible values: True, False1. Relation Operator

= , < , > , <> , <= , >=2. Boolean Operator

AND , OR , NOT

15 = 34 False

15.05 < 17 True

34 < > 34.00002 True

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Truth table

AND ORT T T TT F F TF T F TF F F F

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Boolean Expression

(30 < 15) AND (54 < > 12)

(30 < 35) OR (99 <= 99.80)

FF FFTT ==

TT TTTT ==

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STATEMENT

ASSIGNMENT STATEMENT OUTPUT STATEMENT INPUT STATEMENT

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ASSIGNMENT STATEMENT

For storing the value or a computational result into the variable.

Assignment Statementvariable := expression;

ExampleAREA := X * Y;

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ASSIGNMENT STATEMENT EXAMPLE

From

SUM := SUM + ITEM;SUM := SUM + ITEM;

100100 100100

ITEMITEMSUMSUMBefore ASSIGNMENTBefore ASSIGNMENT

++

200200

SUMSUMAfter ASSIGNMENTAfter ASSIGNMENT

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ASSIGNMENT STATEMENT EXAMPLE

From

AREA := X * Y;AREA := X * Y;

**

AREAAREAXXYY

100100 2020 ??Before ASSIGNMENTBefore ASSIGNMENT

100100 2020 20002000

AREAAREAXXYY

After ASSIGNMENTAfter ASSIGNMENT

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OUTPUT STATEMENT Use following two command for output to

the screen write ( );

After write, remember the location Start at that location for the next time

writeln ( ); When done, go to new line and left side

SyntaxWrite(parameter1, parameter2, …, parametern);Writeln(parameter1, parameter2, …,

parametern);

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EXAMPLE WRITE Write(‘price=‘); {statement 1}Write(’10bt’); {statement 2}

Line1

Before statement 1Before statement 1

Line1 rp eci = After statement 1After statement 1

Line1 rp eci b01= t

After statement 2After statement 2

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EXAMPLE WRITELN Writeln(‘price=‘); {statement 1}Write(’10bt’); {statement 2}

Line1

Before statement 1Before statement 1

After statement 1After statement 1Line1 rp eci =

Line2

b01 t

After statement 2After statement 2Line1 rp eci =

Line2

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Output statement example

Write (‘price =‘, price); Write (‘total = ‘, price); Writeln (‘the total is’,’ ‘, total,

‘unit’); Writeln (‘hello’,’how are you’, ‘doing’);

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Formatted output Integer : width Real_data : width Real_data : width : decimal String_data : width

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Format: Integer Data typeTotal:=2500;Writeln(total:6);

11Line1Line1

11 22 33 44 55 66Line1Line1

0052

11 22 33 44 55 66Line1Line1

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Format: Real Data typePI:=-3.14159;Writeln(PI:9);

11Line1Line1

11 22 33 44 55 99Line1Line1

66 8877

41.3-

11 22 33 44Line1Line1 E

55

+ 0 0

7766 88 99

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Format: Real Data typePI:=3.14159;Writeln(PI:5:2);

11Line1Line1

11 22 33 44 55Line1Line1

41.3

11 22 33 44 55Line1Line1

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Format: String Data typest1:=‘ABC’;Writeln(st1:5);

11Line1Line1

11 22 33 44 55Line1Line1

CBA

11 22 33 44 55Line1Line1

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WHY Output looks like below?

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WHY Output looks like below?

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INPUT STATEMENT

Use following two command for get input from the device into variable read() readln()

Syntax read (parameter1, parameter2, … ); readln (parameter1, parameter2, …);

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INPUT STATEMENT

Exampleread( studentid, course, section);

IF We have input 43650357 204111 15

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INPUT STATEMENT How to input if we use following

statement?read(data1, data2);

Data type Data type 11

Data type Data type 22

INPUTINPUT VALUE VALUE in in

Data1Data1

VALUE VALUE in in

Data2Data2

REMARKREMARK

INTEGER INTEGER 13□15 13 15 Blank is skip

INTEGER CHAR 13□M 13 □ Blank is char

INTEGER STRING 13□AX□

13 □AX□ Blank is part of STRING

For INTEGER, Blank is need for separate numbers.For CHAR/STRING, no blank is need for separate.

521st semester 2004

INPUT STATEMENT What will happened? If Number of input > number of variable

Exceed input will be lost

If Number of input < number of variable Program will pause and wait for the

require input

531st semester 2004

CONCLUSION FROM PREVIOUS

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Conclusions

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CONCLUSIONprogram myFirstProgram;const

myStudentId = 1234567;var

courseTaken: integer;begin

write(‘Please Enter a number of courses’);read(‘courseTaken’);writeln(‘Student’, myStudentId, ‘ takes ’, courseTaken, ‘ courses in this semester’);

end.

Program Heading

Declarations

Program Body

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EXAMPLE PROGRAM 1

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EXAMPLE PROGRAM 2

Problem Write a program for find the area of the circle.

rr

AREA := Pi * Radius * Radius;

a = ¶r2CONSTANTCONSTANT VARIABLEVARIABLE

VARIABLEVARIABLE

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EXAMPLE PROGRAM 2

OUTPUTOUTPUT

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EXAMPLE PROGRAM 3

OUTPUTOUTPUT

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Error 3: Unknown Identifier

num6 is not definednum6 is not definedinin

declaration partdeclaration part

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Error 85: “;” expected.

Current CursorCurrent Cursor

;;

621st semester 2004

Error 94: “.” expected

Have to use .(dot)Have to use .(dot)for the end for the end

of of program bodyprogram body

631st semester 2004

What will we learn in Next Class?

FlowchartIf the Else