CSCI130

1
Lecture-10 (6.1-6.6)

• CSCI130
• Instructor Dr. Imad Rahal

2
Higher-level Programming Languages (PLs)

• Solution to Assignment 3 and class exercise is up
• Exam Chapters 1?5
• Exam policy
• Machine language programming
• limited set of instructions
• binary numbers
• opcodes, absolute memory addresses and data
• Assembly language
• English mnemonics for binary opcodes
• Variables for memory addresses
• limited instruction set
• Use human languages to program
• Large vocabulary (space and time to search)
  opcode lookup
• Synonyms
• Homonyms
• Context

3
Higher-level Programming Languages

• High-level languages are in the middle
• Use English-like phrases and mathematical
  notation
• x x1
• Do it in assembly?
• A limited vocabulary with precise meaning
• Make us think at a higher-level of abstraction
• No attention to technical and hardware details
• Like O.S.
• Does not matter if we have a CISC or RISC
  architecture
• Much larger instruction set for programmers
• Multiplication

4
Translation Programs

• Price for abstraction!
• Unaware of hardware/low-level details
• Higher-level require translation programs
• An example?
• Assembler for assembly
• Fast
• Must be translated to machine language
• It is not trivial as with assembly
• No 1-to-1 correspondence

5
Find the Larger of Two Numbers

• READ
• STOR X
• READ
• STOR Y
• SUB X
• JPOS Y_LARGER
• LOAD X
• WRITE
• HALT
• Y_LARGERLOAD Y
• WRITE
• HALT
• X 0
• Y 0

• In higher-level programming languages, we could
  simply say (4 V.S. 14)
• Read x
• Read Y
• If XgtY, WRITE X
• Else, WRITE Y

6
Show All Numbers Between 1 and N

• READ
• STOR N
• LOOP LOAD COUNT
• ADD VALUE_ONE
• STOR COUNT
• WRITE
• LOAD N
• SUB COUNT
• JPOS LOOP
• HALT
• N 0
• COUNT 0
• VALUE_ONE 1

• Read N (4 V.S. 13)
• For i1 to N
• Write i
• Loop

7
Translation Programs

• Source code (high-level language) ? object code
  (machine language)
• An interpreter does so on a line by line basis
• Redone every time
• Dont have to wait for whole program to be
  translated to see output
• A compiler produces all object code for the given
  source code
• Done once to produce object code
• Must weight
• Read about them in book

8
Algorithms Design

• For the same problem we can have
• Many algorithms to solve it
• Count from 1 to N
• If counter lt N ? loop (or redo)
• If counter gt N ? stoop
• Each implemented through many programs
• Plan to solve a problem vs actual solution in a
  language understood by the computer
• We need to design a clear algorithm
• Pseudo-code (or Flow chart)
• Compromise between English and programming
  language
• Omits details
• Gradual
• Not likely to get it the first time

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Algorithms Design

• Finding the minimum in a list of numbers
• 1-Find the minimum in 1st portion of the list, S1
• 2-Find the minimum in the next portion of the
  list, S2
• 3-Let S be the minimum of S1 and S2
• 4-Repeat steps 2 and 3 until all portions have
  been covered
• 5-S has the minimum
• What is a portion? How do we get it?
• We need more details
• We can assume every position in the list to be a
  portion

10
Algorithms Design

• Psuedocode
• S first number in list
• Do until end of list
• S next number in list
• If S gt S, then S S
• Output S
• Omitted details (depend on the programming
  language)
• What is a list?
• How to know the end of list?
• Ho to go to the next number?
• Now we have an algorithm, but is it right?
• We need to test it

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Algorithms Design

• We usually test by tracing
• Use some values to work thru the algorithm
• 3 23 44 2 12 42 1
• S S Output3 23 3 44 3 22 122 422 1 1

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Computer Programming

• Different types of high-level languages
• The imperative programming paradigm
• Machine language/assembly language
• A program is a sequence of instructions
• Object-oriented paradigm
• Visual Basic or VB uses the OOP
• Objects each having properties and functions
• e.g. car or rabbit
• Properties status, color, model, make, year,
  manual/auto
• Actions turn on, speeds up, slows down, make
  accident, hit rabbit
• An action taken by an object might affect (change
  some property) itself or other objects
• Affect itself turn on CAR
• ? status went from OFF to ON
• Affect other objects hit rabbit
• ? Rabbit is dead but the car is still OK

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Object-Oriented Programming

• Imagine a computer screen with several icons
• Each is a task (object?) also desktop is an
  object
• Each task has its own attributes and functions
• Properties Icon picture/shape and color
• functions
• Single-clicked ? Darken Color (itself)
• Double-clicked ?
• Run corresponding program
• Change desktop look (Desktop is another object)
• The program is collection of interacting objects
• In VB, functions are triggered by events
• Done by users (interactive) e.g. CLICK or
  DOUBLE_CLICK
• Objects sharing properties/methods are grouped
  into classes
• Object My Documents, My Computer
• Class Desktop Icon

14
Steps in Writing a Program

• Read In Book
• Steps in Writing a Program
• OO Applications Development

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Introduction

• Basic is an imperative language developed in
  1960s
• Visual Basic (VB) --- developed by Microsoft
• OO version of Basic
• Underlying ALL MS office programs
• You could do a lot
• Write your own programs
• Tailor office applications
• Can be used to link many applications together
• Visually oriented
• Programs have a GUI for input/output
• Not a command prompt
• First thing to do to build a VB program is to
  design the interface