Our brains run without being told to run'

1
Lecture 3

• Our brains run without being told to run.
• Douglas Hofstadter, Godel, Escher, Bach

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Concepts from lecture 2
3
Concepts from lecture 2

• reserved words
• identifiers
• variables
• built in functions
• program output
• basic types

4
Quiz 1 (10 minutes )

• Write Pascal program which computes and outputs
  the area of triangle given base and height.
• Define algorithm
• Who was Pascal?

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String constants

• Used them without noticing
• Examples
• Hello world
• My name is
• My salary is

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Arithmetic operations

• Absolutely need them
• issue order of operations

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Example for order of operations

• PROGRAM LineEquation
• VAR iX1, iY1, iX2, iY2 integer
• VAR iSlope, iYIntersept integer
• BEGIN
• iX1 2
• iY1 3
• iX2 5
• iY2 -4
• iSlope ( iY2 - iY1 ) DIV ( iX2 - iX1 )
• iYIntersept ( iY1iX2 - iX1iY2 ) DIV (
  iX2 - iX1 )
• writeln( 'The equation of a line is ')
• writeln( 'y ', iSlope, 'x ',
  iYIntersept )
• END.

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DIV and MOD

• A BX C

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Mixing types

• PROGRAM MixingTypes
• VAR iA, iB integer
• VAR rX, rY real
• BEGIN
• iA 2
• iB 3
• rX 2.43
• rY iA( iB DIV iA - rX )
• writeln( 'y ', rY )
• END.

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What about input?

• we need to be able to supply different data
• input device is keyboard
• built-in function readln

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Readln example

• PROGRAM InteractiveLineEquation
• VAR rX1, rY1, rX2, rY2 real
• VAR rSlope, rYIntersept real
• BEGIN
• write('Enter first known point ')
• readln( rX1, rY1 )
• write('Entee\r second known point ')
• readln( rX2, rY2 )
• rSlope ( rY2 - rY1 ) / ( rX2 - rX1 )
• rYIntersept ( rY1rX2 - rX1rY2 ) / ( rX2
  - rX1 )
• writeln( 'The equation of a line is ')
• writeln( 'y ', rSlope, 'x ',
  rYIntersept )
• END.

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Constants

• is really a constant not a variable
• special reserved word CONST

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Example of a constant

• PROGRAM AreaOfCircleWithConstantPi
• VAR rRadius, rArea, rCircumference real
• CONST PI 3.14159
• BEGIN
• rRadius 5.0
• rArea PI rRadius rRadius
• rCircumference 2 PI rRadius
• writeln( 'The area of a circle with radius
  ', rRadius52,
• ' is equal to ',
  rArea63 )
• writeln( 'and circumference is equal to ',
  rCircumference63 )
• END.

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Grade computation program

• PROGRAM GradeComputation
• VAR iHw1, iHw2, iHw3, iHw4, iHw5, iHw6, iHw7
  integer
• VAR iMidterm1, iMidterm2, iFinal, iHwScore
  integer
• VAR rHwAverage, rTotalScore, rTotalPercent
  real
• CONST NUMBER_OF_HOMEWORKS 7 MAXIMUM_SCORE
  134
• BEGIN
• write('Enter your homework grades ')
• readln( iHw1, iHw2, iHw3, iHw4, iHw5, iHw6,
  iHw7 )
• write('Enter your midterm grades ')
• readln( iMidterm1, iMidterm2 )
• write('Enter your final grade ')
• readln( iFinal )
• iHwScore iHw1 iHw2 iHw3 iHw4 iHw5
  iHw6 iHw7
• rHwAverage iHwScore / NUMBER_OF_HOMEWORKS
• rTotalScore 0.2iHwScore0.4(iMidterm1iMi
  dterm2)0.4(iFinal)
• rTotalPercent rTotalScore/MAXIMUM_SCORE100
  

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Grade computation (part 1)

• PROGRAM GradeComputation
• VAR iHw1, iHw2, iHw3, iHw4, iHw5, iHw6, iHw7
  integer
• VAR iMidterm1, iMidterm2, iFinal, iHwScore
  integer
• VAR rHwAverage, rTotalScore, rTotalPercent
  real
• CONST NUMBER_OF_HOMEWORKS 7 MAXIMUM_SCORE
  134
• BEGIN
• write('Enter your homework grades ')
• readln( iHw1, iHw2, iHw3, iHw4, iHw5, iHw6,
  iHw7 )
• write('Enter your midterm grades ')
• readln( iMidterm1, iMidterm2 )
• write('Enter your final grade ')
• readln( iFinal )

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Grade computation (part 2)

• iHwScore iHw1 iHw2 iHw3 iHw4 iHw5
  iHw6 iHw7
• rHwAverage iHwScore / NUMBER_OF_HOMEWORKS
• rTotalScore 0.2iHwScore0.4(iMidterm1iMi
  dterm2)0.4(iFinal)
• rTotalPercent rTotalScore/MAXIMUM_SCORE100
  
• writeln( 'Homework score ', iHwScore )
• writeln( 'Homework average ', rHwAverage63
  )
• writeln( 'Total score ', rTotalScore63 )
• writeln( 'Total percent ',
  rTotalPercent63, '' )
• END.

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String variables

• collections of characters
• sequential

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String program

• PROGRAM StringProgram
• VAR sLast, sFirst string10
• VAR cFirstChar char
• BEGIN
• sFirst 'Blaise'
• sLast 'Pascal'
• writeln( 'Pascal programming language is
  named' )
• writeln( 'after French mathematician ',
  sFirst, ' ', sLast )
• cFirstChar sLast 1
• writeln( 'Look him under ''', cFirstChar,
  ''' in encyclopedia.' )
• END.

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Homework

• Read Chapter 3
• Problem 14, page 99
• (TO BE HANDED IN) next Monday, October 4

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Programs for this lecture

• Linear equation
• Mixing types
• Interactive line equation
• Constant Illustration
• Grade computation
• String program