Programming

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Programming

• HSPM J713

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Programming languages and systems

• Programming languages generally come with
  programming system
• The language part of a programming language is
  the key words, symbols, and syntax used to write
  code.
• The system part translates the written code into
  machine instructions that computer executes. Can
  be a compiler or an interpreter.

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Platform-specific

• Language system works with specific hardware
• The IBM-compatible PC or the Windows PC
• All use the same
• Machine instructions (which depends on chip
  architecture)
• Memory, screen

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Assembly language

• mov ax, 1234h
• mov bx, ax
• Directly translates into machine code (binary
  numbers)
• Compiler translates all instructions in program
  into machine code
• Low level explicitly manipulates registers
  (places to hold data) on the CPU chip.
• Each chip has its own assembly language

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FORTRAN

• Do 10 j 2 , 1000
• B(j) A(j-1)
• A(j-1)j
• 10 continue
• Compiled into machine language and then run
• Used on mainframes since 1950s.
• Designed for math

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BASIC

• Beginner's All-purpose Symbolic Instruction Code
• For students and general users
• Interpreted One line at a time is translated
  into machine code and executed

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BASIC unstructured, interpreted

• 10 INPUT "What is your name ", U
• 20 PRINT "Hello " U
• 30 INPUT "How many stars do you want ", N
• 40 S ""
• 50 FOR I 1 TO N
• 60 S S ""
• 70 NEXT I
• 80 PRINT S
• 90 INPUT "Do you want more stars? ", A
• 100 IF LEN(A) 0 THEN 90
• 110 A LEFT(A, 1)
• 120 IF A "Y" OR A "y" THEN 30
• 130 PRINT "Goodbye "U
• 140 END

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BASIC structured, compiled

• INPUT "What is your name ", UserName
• PRINT "Hello " UserName
• DO
• INPUT "How many stars do you want ", NumStars
• Stars STRING(NumStars, "")
• PRINT Stars
• DO
• INPUT "Do you want more stars? ", Answer
• LOOP UNTIL Answer ltgt ""
• Answer LEFT(Answer, 1)
• LOOP WHILE UCASE(Answer) "Y"
• PRINT "Goodbye " UserName

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C, C

• This Hello world program uses the C standard
  library stream facility to write a message to
  standard output
• include ltiostreamgt // provides stdcout
• int main()
• stdcout ltlt "Hello, world!\n"
• Uses library of code, callable with key words,
  to execute complex tasks
• Compiler for specific platform translates that
  into machine code.

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Java

• Compiled code runs on Virtual Machine
• A virtual machine is written for each platform.
• The virtual machine for a platform translates
  virtual machine instructions into machine
  instructions for that platform
• Java runs on PC virtual machine on PCs,
  Macintosh virtual machine on Macs, for example.
• So compiled Java code can run on many platforms.
  Good for web applications.

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Java resembles C in syntax

• Class HelloWorld
• public static void main (String arguments)
• System.out.println(Hello World!)
• Compiled using Java Development Kit

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Java uses objects

• import java.applet.
• import java.awt.
• public class TextEntry extends Applet
• TextField Reply
• TextField Entry
• public void init()
• setBackground(Color.white)
• add("EntryLabel", new Label("Type your number
  in the small box and press Enter"))
• add("Entry", Entry new TextField("", 5))
• add("Reply", Reply new TextField("My reply
  will appear here.", 60))
• Reply.setEditable(false)
• public void compute()
• int value
• try
• value Integer.valueOf(Entry.getText().trim())
  .intValue()

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Java uses objects

• import java.applet.
• import java.awt.
• public class TextEntry extends Applet
• TextField Reply
• TextField Entry

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Java uses objects

• public class TextEntry extends Applet
• TextField Reply
• TextField Entry
• public void init()
• setBackground(Color.white)
• add("EntryLabel", new Label("Type your number
  in the small box and press Enter"))
• add("Entry", Entry new TextField("", 5))
• add("Reply", Reply new TextField("My reply
  will appear here.", 60))
• Reply.setEditable(false)

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Java uses objects

• public void compute()
• int value
• try
• value Integer.valueOf(Entry.getText().trim())
  .intValue()
• if (value 15) Reply.setText("Correct!
  15 is right!")
• else
• if (value gt 15) Reply.setText(Entry.getText()
  " is too high.")
• if (value lt 15) Reply.setText(Entry.getText()
  " is too low.")
• catch(NumberFormatException e)
  Reply.setText(Entry.getText() " is not a
  number.")
• public boolean action(Event e, Object dummy)
• compute()
• return(true)