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# Introduction to Programming - PowerPoint PPT Presentation

Introduction to Programming. Prof. George Zolla Prof. Gary Porter (IS 2020). Programs. 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. Programming Languages.

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### Introduction to Programming

Prof. George Zolla

Prof. Gary Porter (IS 2020)

.

• 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.

• A program can only instruct a computer to:

• Sequence

• Calculate

• Store data

• Compare and branch

• Iterate or Loop

• Write Output

• Sequence control structures direct the order of program instructions.

• The fact that one instruction follows another—in sequence—establishes the control and order of operations.

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

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

Place 1 in Counter

• 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

false

true

Exit

True statement a

IF-THEN

Test condition p

Test condition p

false

true

“false” statement a

“true” statement a

Exit

IF-THEN-ELSE

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

No

• Iteration control structures are looping mechanisms.

• Loops repeat an activity until stopped. The location of the stopping mechanism determines how the loop will work:

• Trailing 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.

Exit

No

Test condition p

Yes

Loop statement a

DO WHILE Loop

• 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.

Exit

No

Yes

Test condition p

DO UNTIL Loop

Loop statement a

Programs are Solutionsto Problems

• Programmers arrive at these solutions by using one or more of these devices:

• Logic flowcharts

• Structure charts

• Pseudocode

• Structured Programming

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

Terminator. Shows the starting and ending points of the program. A terminator has flowlines in only one direction, either in (a stop node) or out (a start node).

Data Input or Output. Allows the user to inputdata and results to be displayed.

Processing. Indicates an operation performed by the computer, such as a variable

assignment or mathematical operation.

Decision. The diamond indicates a decision structure. A diamond always has two

flowlines out. One flowlineout is labeled the “yes” branch and the other is labeled the

“no” branch.

Predefined Process. One statement denotes a group of previously defined statements.

For instance, “Calculate m!” indicates that the program executes the necessary commands

to compute m factorial.

Connector. Connectors avoid crossing flowlines, making the flowchart easier to read.

Connectors indicate where flowlines are connected. Connectors come in pairs, one with

a flowline in and the other with a flowline out.

Off-page connector. Even fairly small programs can have flowcharts that extend several

pages. The off-page connector indicates the continuation of the flowchart on another

page. Just like connectors, off-page connectors come in pairs.

Flowline. Flowlines connect the flowchart symbols and show the sequence of operations during the program execution.

Common Flowchart Symbols

sum=0

Input price

sum=sum+price

More

items?

Yes

No

tax=sum x 0.0725

total=sum+tax

Output sum, tax,

and total

Stop

Flowchart for aCash Register Program

• Structure charts illustrate the structure of a program by showing independent hierarchical steps.

• Major divisions are subdivided into smaller pieces of information.

• This device is not visual but is considered a “first draft” of the actual program.

• Pseudocode is written in the programmer’s native language and concentrates on the logic in a program—not the syntax of a programming language.

Pseudocode for aCash Register Program

sum=0

While More items do

Input price

sum=sum+price

End While

tax=sum x 0.0725

total=sum+tax

Output sum, tax, total

• 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.

Analyze the problem

Design the solution algorithm

Design the user interface

Write the code

Test and debug the program

Complete the documentation

• Machine language

• Assembly Language

• High Level Languages

• Fourth Generation Languages (4GL)

• different for each computer processor

0100

001101 100000 001101 110001

00101 10001 10000

01110

111001

. . .

• different for each computer processor

main proc pay

mov ax, dseg

mov ax, 0b00h

mov a1, b1

mul b1, ax

mov b1, 04h

• 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 .

• Interpreter

• Translates instructions to machine code line-by-line.

• Compiler

• Translates the entire program to machine code before running it.

• Machine language

• Procedure-oriented languages

• Object-oriented languages

• Event-driven languages

• FORTRAN

• COBOL

• Pascal

• C

• Object-oriented languages

• Smalltalk

• C++

• Event-driven languages

• Visual Basic

• most Visual languages

Program - detailed set of instructions for a computer

Programming Language - tool used to create a program; defined by semantics and syntax

Semantics- the meaning of words in a language

Syntax- rules for combining symbols of a language

Source Code (code) - program you write using a programming language

Interpreter- translates and executes source code statement by statement

Interpreter Process

Compiler Process