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# CMP 131 Introduction to Computer Programming - PowerPoint PPT Presentation

CMP 131 Introduction to Computer Programming. Violetta Cavalli-Sforza Week 5, Lecture 1 (Monday). THIS WEEK. Homework #2: Turn in the non-programming part today (in class or by e-mail after class).

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### CMP 131Introduction to Computer Programming

Violetta Cavalli-Sforza

Week 5, Lecture 1 (Monday)

• Homework #2:

• Turn in the non-programming part today (in class or by e-mail after class).

• Can keep working on the programming part through the March 29, but you must send it to me by March 29 midnight. This includes part b) Exercises 8 & 13.

• Makeup session:

• Tuesday March 27, 6:30-8pm, LAB 01

• Quiz #2 on Wednesday

• Will cover material through today.

• Pascal Data Types

• Real

• Ordinal Data Types

• Integer

• Character

• Boolean

• Expressions again

• Assignment statement again

• Input/Output and formatting

• Ordinal:

• integer

• char

• boolean

• Non-ordinal:

• real

• strings ( added to Turbo Pascal)

• A type Integer object represent only whole numbers.

• Not all integer range can be represented inside a computer.

• On each system, the predefined constant MaxInt is the largest possible integer. The smallest integer is -MaxInt-1

• What kinds of Objects can be Integers?

• Variables

• Constants

• Literals

Have names associated with them. They are defined (constants) or declared (variables) in the program declaration section.

Appear directly as values of constants or in program without being defined or declared.

• Arithmetic: + - * / div mod

• div computes the integral part of the result of dividing the first operand by the second.

• mod returns the integer remainder of the result of dividing its first operand by its second.

• divandmodare integer operators only!

• they expect integer operands

• they return an integer result

• Comparison Pperators: =, <>, <=, >=, < , >

• Assignment: :=

• Standard Functions: pred, succ, others…

• Examples:

3 div 15 = 0 3 div -15 = 0

15 div 3 = 5 15 div -3 = -5

16 div 3 = 5 16 div -3 = -5

17 div 3 = 5 -17 div 3 = -5

18 div 3 = 6 -18 div -3 = 6

3 mod 5 = 3 5 mod 3 = 2 -5 mod 3 = -2

4 mod 5 = 4 5 mod 4 = 1 -5 mod 4 = -1

5 mod 5 = 0 15 mod 5 = 0 -15 mod 5 = 0

6 mod 5 = 1 15 mod 6 = 3 -15 mod 6 = -3

7 mod 5 = 2 15 mod 7 = 1 -15 mod -7 = -1

8 mod 5 = 3 15 mod 8 = 7 15 mod 0 = ??

• ?? Means “Undefined”

• For div, the sign of the result depends on the signs of the operands, just like for regular division

• For mod, the sign of the result only depends on the sign of the dividend

PROGRAM intdiv;

VAR a, b: integer;

BEGIN

REPEAT

write('Input a and b: '); readln(a,b);

IF b <> 0 THEN

writeln('DIV = ', a DIV b, ' MOD = ', a MOD b);

writeln;

UNTIL b = 0;

END.

• Used to store any single character value.

• Values: 0 to 255, map to specific characters according to the ASCII coding system.

• Ex. ‘a’, ‘A’, ‘.’, ‘,’, ‘#’,’1’, ‘0’, …

• Character literals must be enclosed in apostrophes.

• The blank characters is written as ' '.

• You don't type apostrophes around character data entered at the terminal.

• Blank character is entered by pressing the space bar.

• Operations:

• Assignment: :=

• Comparison Operators: =, <>, <=, >=, < , >

• Standard Functions: pred, succ

PROGRAM CharComp;

VAR firstchar, secondchar: char;

BEGIN

write('Enter a character, without quotes > ');

write('Enter another character, without quotes > ');

IF firstchar = secondchar

THEN writeln(firstchar,' is equal to ', secondchar)

ELSE

IF firstchar < secondchar

THEN writeln(firstchar,' is less than ', secondchar)

ELSE writeln(firstchar,' is greater than ', secondchar);

END.

PROGRAM CharOrd;

VAR ch: char;

BEGIN

write('Enter a character, without quotes > ');

writeln('The successor of ',ch,' is ',succ(ch));

writeln('The predecessor of ',ch,' is ',pred(ch));

END.

• Values:

• true (1) & false (0)

• Operations:

• Assignment: :=

• Comparison Operators: =, <>

• (the others are not useful)

• Logical: AND, NOT, OR (in expressions)

• Standard Procedurs:

• Display with write, writeln

• (Not read !!!) – ‘false’ and ‘true’ are string literals, not the boolean values false and true

PROGRAM BoolOrd;

BEGIN

writeln('The successor of ',false,' is ',succ(false));

writeln('The predecessor of ',false,' is ',pred(false));

writeln('The successor of ',true,' is ',succ(true));

writeln('The predecessor of ',true,' is ',pred(true));

END.

PROGRAM CharOrd;

VAR ch: char;

BEGIN

write('Enter a character, without quotes > ');

writeln('The successor of ',ch,' is ',succ(ch));

writeln('The predecessor of ',ch,' is ',pred(ch));

END.

• Sequence of characters enclosed in (‘) apostrophes (single quotes).

• Literals Ex. : ‘Please enter a number > ‘

• Constants, Ex: CONST Border = ‘======‘

• Variable, Ex: VAR InputString : string;

• Up to 255 characters.

• For Turbo Pascal only

• Operations:

• Store in memory

• Compare

• Display

• An expression is:

• a single value (variable, constant, literal)E.g. MyVar, MyConst, ‘my literal’, 5

• 2 or more values are combined to produce a single value.E.g. MyVar – MyConst + 5

• In constant definitions, but must use only constant arguments, E.g.

• Three = 1 + 2;

• CONST One = 1; Two = 2; Three = One + Two;

• On the right hand side of an assignment statement, e.g.

• Sum := Sum + NewValue;

• As arguments to write, writeln, and other standard and user-defined procedures and functions.

• Elsewhere in different kinds of statements

• Expressions are made up of operands and operators.

• Each operand in an expression has a type.

• Operators expect operands of specific type(s)

• Operators return a result of a specific type.

• Rules govern:

• priority of different types of operators and order of evaluation within the same priority class

• what operand types may be combined with a specific operator

• what the type of the result is

• Depends on its operands.

• Of type Integer only if all its operands are type integer and none of its operators is / (real division).

• Mixed type expression: ex. 5.2 + 4

• Contains both Integer & Real operands.

• Mixed-type assignment:

• Assignment of an expression of one type to a variable of a different type. Ex. VAR r: Real; … r := 4 + 2;

• Real expression can’t be assigned to a type Integer variable.

• Parenthesized subexpressions must be evaluated separately.

• For nested parenthesized sub-expressions, the innermost sub-expression evaluated first.

• Left associative rule:

• Operators in the same subexpression and at the same precedence level are evaluated left to right.

• / operator always yields a real value

• mod and div can only be used with integers

• Integer:

• ( ) : Evaluate from inside out

• Unary + unary -

• * , MOD, DIV : Evaluate from left to right

• Binary + and - : Evaluate from left to right

• Real:

• () : Evaluate from inside out

• Unary + and unary -

• * , / : Evaluate from left to right

• + , - : Evaluate from left to right

/

*

*

+

-

Rules for Expression Evaluation

• Example:

X * Y * Z + A / B - C * D ==>

((((X * Y) * Z) + (A / B)) - (C * D))

• Can also be drawn to show the sequence of evaluation

• Nodes are for operators

• Lines are for operands

X * Y * Z + A / B - C * D

• What are the results of the following expressions?

22 div 7 7 div 22 22 mod 7 7 mod 22

• What is valid & what is invalid in the following

const PI = 3.14159;

MaxI = 1000;

var X, Y : Real;

A, B, I : Integer;

. . .

I := A mod B; I := A mod Y;

X := A / B; I := A / B; X := A / Y;

I := B div 0; I := A mod 0; X := PI div Y;

X := A mod (A / B);

I := (MaxI - 990) div A;

I := A mod (MaxI - 990);

SEE TURBO PASCAL COMPILATION ERRORS

CONST PI = 3.14159;

MaxI = 1000;

VAR X, Y : Real;

A, B, I : Integer;

BEGIN

I := A mod B;

{ I := A mod Y; }

X := A / B;

{ I := A / B; }

X := A / Y;

{ I := B div 0; }

I := A mod 0;

{ X := PI div Y; }

{ X := A mod (A / B); }

I := (MaxI - 990) div A;

I := A mod (MaxI - 990);

END.

• Rules:

• Use the * operator to indicate multiplication.

• Use parentheses when required to control the order of operator evaluation.

• Never write two arithmetic operators in succession; they must be separated by an operand or an open parenthesis.

• All assignment statements must be written in a linear form. Parentheses are often needed to separate numerator from the denominator involved in divisions.

• Examples:

• Assignment

• Output Operations: Write, Writeln

• Output formatting with write/writeln

• Assignment statement:

• Instruction that stores a value or a computational result in a variable

• Used to perform computations

• Syntax: <result> := <expression>

• The variable specified by the result is assigned the value of the expression.

• Previous value of result is destroyed.

• Assignment symbol ‘:=‘ is not an algebraic equation.

• Value being assigned must be assignment compatible with the variable receiving it.

• Examples:

• Valid assignments

X := Y + Z + 2.0;

Sum := Sum + Item;

NewX := - X;

SqYards := MetersToYards * SqMeters;

• Invalid assignments

Ch := 5; { Ch is of char type }

Ch := Name; { Name is of string type }

Name := True; { True is a Boolean literal }

BoolVar := ‘False’; {‘ False’ is a string literal }