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CMP 131 Introduction to Computer Programming

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Title: CMP 131 Introduction to Computer Programming


1
CMP 131Introduction to Computer Programming
  • Violetta Cavalli-Sforza
  • Week 5, Lecture 1 (Monday)

2
THIS WEEK
  • 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, 630-8pm, LAB 01
  • Quiz 2 on Wednesday
  • Will cover material through today.

3
TODAY
  • Pascal Data Types
  • Real
  • Ordinal Data Types
  • Integer
  • Character
  • Boolean
  • Expressions again
  • Assignment statement again
  • Input/Output and formatting

4
Predefined data types
  • Ordinal
  • integer
  • char
  • boolean
  • Non-ordinal
  • real
  • strings ( added to Turbo Pascal)

5
Integer Data Type
  • 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.
6
Operations in Integer
  • 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.
  • div and mod are integer operators only!
  • they expect integer operands
  • they return an integer result
  • Comparison Pperators , ltgt, lt, gt, lt , gt
  • Assignment
  • Standard Procedures ReadLn, WriteLn, Read, Write
  • Standard Functions pred, succ, others

7
Integer Data Type
  • 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

8
Try running this program
  • PROGRAM intdiv
  • VAR a, b integer
  • BEGIN
  • REPEAT
  • write('Input a and b ') readln(a,b)
  • IF b ltgt 0 THEN
  • writeln('DIV ', a DIV b, ' MOD ', a
    MOD b)
  • writeln
  • UNTIL b 0
  • END.

9
Character Data Type
  • 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 , ltgt, lt, gt, lt , gt
  • Standard Procedures read, readln, write, writeln
  • Standard Functions pred, succ

10
Comparing Characters
  • PROGRAM CharComp
  • VAR firstchar, secondchar char
  • BEGIN
  • write('Enter a character, without quotes gt ')
  • readln(firstchar)
  • write('Enter another character, without quotes
    gt ')
  • readln(secondchar)
  • IF firstchar secondchar
  • THEN writeln(firstchar,' is equal to ',
    secondchar)
  • ELSE
  • IF firstchar lt secondchar
  • THEN writeln(firstchar,' is less than ',
    secondchar)
  • ELSE writeln(firstchar,' is greater than
    ', secondchar)
  • readln
  • END.

11
Character Ordering
  • PROGRAM CharOrd
  • VAR ch char
  • BEGIN
  • write('Enter a character, without quotes gt ')
  • readln(ch)
  • writeln('The successor of ',ch,' is
    ',succ(ch))
  • writeln('The predecessor of ',ch,' is
    ',pred(ch))
  • readln
  • END.

12
Boolean Data Type
  • Values
  • true (1) false (0)
  • Operations
  • Assignment
  • Comparison Operators , ltgt
  • (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

13
Comparing Booleans
  • 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))
  • readln
  • END.

14
Boolean Ordering
  • PROGRAM CharOrd
  • VAR ch char
  • BEGIN
  • write('Enter a character, without quotes gt ')
  • readln(ch)
  • writeln('The successor of ',ch,' is
    ',succ(ch))
  • writeln('The predecessor of ',ch,' is
    ',pred(ch))
  • readln
  • END.

15
String Data Type
  • Sequence of characters enclosed in ()
    apostrophes (single quotes).
  • Literals Ex. Please enter a number gt
  • Constants, Ex CONST Border
  • Variable, Ex VAR InputString string
  • Up to 255 characters.
  • For Turbo Pascal only
  • Operations
  • Read
  • Store in memory
  • Compare
  • Display

16
Expressions
  • 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

17
Expressions Occur
  • 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.
  • Area PI Radius Radius
  • Sum Sum NewValue
  • As arguments to write, writeln, and other
    standard and user-defined procedures and
    functions.
  • Elsewhere in different kinds of statements

18
Operands,Operators,Types
  • 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

19
Expression Types
  • 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 cant be assigned to a type
    Integer variable.

20
Expression Evaluation
  • 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

21
Operand Priority
  • 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

22
Rules for Expression Evaluation
  • Example
  • X Y Z A / B - C D gt
  • ((((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

23
Self-Check
  • 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

24
  • PROGRAM Types
  • 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.

25
Pascal Mathematical Formulas
  • 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

Mathematical formula Pascal expression
b2 - 4ac a b c d a ? r2 a ? -(b c) B B - 4 A C (A B ) / ( C D ) A PI Radius Radius A (- ( B C) )
26
Simple Statements
  • Assignment
  • Input Operations Read, Readln
  • Output Operations Write, Writeln
  • Output formatting with write/writeln

27
Assignment Statement
  • Assignment statement
  • Instruction that stores a value or a
    computational result in a variable
  • Used to perform computations
  • Syntax ltresultgt ltexpressiongt
  • Example Area PI Radius Radius
  • 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.

28
Assignment Statement
  • 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
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