CMP 131 Introduction to Computer Programming

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CMP 131Introduction to Computer Programming

• Violetta Cavalli-Sforza
• Week 5, Lecture 1 (Monday)

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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.

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TODAY

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

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Predefined data types

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

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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.
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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

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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

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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.

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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

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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.

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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.

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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

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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.

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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.

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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

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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

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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

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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

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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.

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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

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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

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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

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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

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• 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.

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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) )
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Simple Statements

• Assignment
• Input Operations Read, Readln
• Output Operations Write, Writeln
• Output formatting with write/writeln

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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.

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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