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Programming Languages

• A program is a set of step-by-step instructions
  that directs the computer to do the tasks you
  want it to do and produce the results you want.
• A programming language is a set of rules that
  provides a way of telling a computer what
  operations to perform.

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What Can a Program Do?

• A program can only instruct a computer to
• Read Input
• Sequence
• Calculate
• Store data
• Compare and branch
• Iterate or Loop
• Write Output

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Sequence Control Structures

• Sequence control structures direct the order of
  program instructions.
• The fact that one instruction follows anotherin
  sequenceestablishes the control and order of
  operations.

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Calculate

• A program can instruct a computer to perform
  mathematical operations.

Add 1 to Counter
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Store

• A program will often instruct a computer to store
  intermediate results.

Place 1 in Counter
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Compare and Branch

• A program can instruct a computer to compare two
  items and do something based on a match or
  mismatch which, in turn, redirect the sequence of
  programming instructions.
• There are two forms
• IF-THEN
• IF-THEN-ELSE

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IF-THEN
Test condition p
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IF-THEN-ELSE
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Iterate

• A program loop is a form of iteration. A computer
  can be instructed to repeat instructions under
  certain conditions.

No
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Iteration Control Structures

• Iteration control structures are looping
  mechanisms.
• Loops repeat an activity until stopped. The
  location of the stopping mechanism determines how
  the loop will work
• Leading decisions
• Trailing decisions

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Leading Decisions

• If the stop is at the beginning of the iteration,
  then the control is called a leading decision.
• The command DO WHILE performs the iteration and
  places the stop at the beginning.

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DO WHILE Loop
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Trailing Decisions

• If the stop is at the end of the iteration, the
  control mechanism is called a trailing decision.
• The command DO UNTIL performs the iteration and
  puts the stop at the end of the loop.

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DO UNTIL Loop
Loop statement a
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Programs are Solutionsto Problems

• Programmers arrive at these solutions by using
  one or more of these devices
• Logic flowcharts
• Structure charts
• Pseudocode
• Structured Programming

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Logic Flowcharts

• These represent the flow of logic in a program
  and help programmers see program design.

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Common Flowchart Symbols
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Flowchart for aCash Register Program
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Structure Charts

• Structure charts illustrate the structure of a
  program by showing independent hierarchical
  steps.
• Major divisions are subdivided into smaller
  pieces of information.

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Psuedocode

• This device is not visual but is considered a
  first draft of the actual program.
• Pseudocode is written in the programmers native
  language and concentrates on the logic in a
  programnot the syntax of a programming language.

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Pseudocode for aCash Register Program
sum0 While More items do Input price
sumsumprice End While taxsum x
0.0725 totalsumtax Output sum, tax, total
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Structured Programming

• Structured program languages lend themselves to
  flowcharts, structure charts, and pseudocode.
• Structured programming languages work best where
  the instructions have been broken up into small,
  manageable parts.

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The Program Development Cycle
Analyze the problem
Design the solution algorithm
Design the user interface
Write the code
Test and debug the program
Complete the documentation
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Levels of Programming Languages

• Machine language
• Assembly Language
• High Level Languages
• Fourth Generation Languages (4GL)

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Machine Languages

• different for each computer processor
• 0100
• 001101 100000 001101 110001
• 00101 10001 10000
• 01110
• 111001
• . . .

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Assembly Languages

• different for each computer processor
• main proc pay
• mov ax, dseg
• mov ax, 0b00h
• add ax, dx
• mov a1, b1
• mul b1, ax
• mov b1, 04h

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High-Level Languages

• Higher Level Languages
• Use traditional programming logic where the
  programming instructions tell the computer what
  to do and how to perform the required operations.
• 4GLs
• Use high-level English-like instructions to
  specify what to do, not how to do it .

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PL hierarchy
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Interpreter vs Compiler

• Interpreter
• Translates instructions to machine code
  line-by-line.
• Compiler
• Translates the entire program to machine code
  before running it.

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Interpreter Process
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Compiler Process
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Types of Programming Languages

• Machine language
• Procedure-oriented languages
• Object-oriented languages
• Event-driven languages

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Procedure-Oriented Languages

• FORTRAN
• COBOL
• Pascal
• C
• Ada

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OOED Languages

• Object-oriented languages
• Smalltalk
• C
• Java
• Event-driven languages
• Visual Basic
• most Visual languages