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The Art of Programming

Programming Languages

Flowcharts

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First and Foremost: HOW ARE PROGRAMS EXECUTED???

Program = a set of instructions

How are those instructions carried out?

1- FETCH CYCLE: To be executed, an instruction must first be retrieved from primary storage

Program counter is a special register in the CPU that always holds the address of the next instruction to be carried out !

Then, the instruction must be decoded

2- EXECUTION CYCLE:The instruction can now be executed.First, data is obtained from memory and sent to ALU for processingThen, operation is performed.

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The Program Development Process

1- Defining the problem

2- Specifying the software requirements

3- Designing the program (the algorithm, the flowchart, logic)

4- Coding the program (programming language)

5- Testing the program (debugging)

6- Installing and maintaining the program

7- Documenting the program

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A successful program must be

correct

usable

reliable

understandable

modifiable

maintainable

flexible

general

efficient

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The Program Development Process

1- Defining the problem

2- Specifying the software requirements

Desired output : content? Format? Output devices?

Required input: data? Accessibility? Format?

Necessary processing: process, user interface, equipment

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3- Designing the program (the algorithm, the flowchart, logic)

ALGORITHM = step-by-step method for getting from input to output

PSEUDOCODE = an informal yet structured expression of algorithm

Programming languages have specific grammar and syntaxPseudocode imitates the programming languages, but is informal

FLOWCHART = a graphic form of an algorithm

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Terminal symbol indicates the beginning or end

Flowlines indicate the order of operations

Process symbol stands for program instructions

Input/output symbol represents any instruction to accept input data or present output data

Decision symbol marks a branching point, where the flow is directed to one branch or the other based on the answer to a YES/NO question

FLOWCHART SYMBOLS

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Programming as Process Design

Problem: determining the factorial of a number (ex: 5!)

A human would probably arrange the problem as

5 ! = 5 x 4 x 3 x 2 x 1= 20 x 6= 120

A computer, on the other hand, would do the same probably as:•Assign 1 to a variable A. •Assign 1 to a variable B. •Multiply the value of A (1) by the value of B (1) (yielding 1) and assign that value to B. •Add 1 to the value of A (1) (yielding 2) and assign that value to A. •Multiply the value of A (2) by the value of B (1) (yielding 2) and assign that value to B. •Add 1 to the value of A (2) (yielding 3) and assign that value to A. •Multiply the value of A (3) by the value of B (2) (yielding 6) and assign that value to B. •Add 1 to the value of A (3) (yielding 4) and assign that value to A. •Multiply the value of A (4) by the value of B (6) (yielding 24) and assign that value to B. •Add 1 to the value of A (4) (yielding 5) and assign that value to A. •Multiply the value of A (5) by the value of B (24) (yielding 120) and assign that value to B. •Add 1 to the value of A (5) (yielding 6) and assign that value to A. •The value stored in variable B (120) is the factorial.

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The algorithm for these steps is something like this:

1. Assign 1 to a variable A.

2. Assign 1 to a variable B.

3. Test whether the value of variable A is greater than n, the number for which the factorial is to be found. If so, continue with step 7. Otherwise, continue with the next step.

4. Form the product of the value of the variable A and the value of the variable B, and assign that product to the variable B.

5. Form the sum of the value of the variable A and the constant 1, and assign that sum to the variable A.

6. Continue with step 3.

7. The factorial is the value of the variable B.

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The Flowchart for this algorithm :

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The following represents the same algorithm in the JavaScript language:

function Factorial (x){

var f = 1;

for (var i = 1; i <= x; i ++){

f = f * i;}

return f;}

The following represents the same algorithm in Visual Basic for Applications:

Private Function Factorial(ByVal n As Long) As Double

Dim lIndex As LongDim dProduct As Double

dProduct = 1For lIndex = 1 To n

dProduct = dProduct * lIndexNext lIndex

Factorial = dProductEnd Function

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The following represents the same algorithm in the MSWLOGO language:

to factorial :valuemake "product 1make "i :valuewhile [:i > 1] [

make "product :product * :imake "i :i - 1]

print :productend

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Coding the Program

Code = process of expressing the fully detailed algorithm in a standard programming language

Programming languages have their own format and SYNTAX

SYNTAX = vocabulary, grammar and punctuation

Source code is usually entered in the keyboard via a text editor

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Programming Building Blocks

Comments and white space

Data types

Numbers

Variables and assignment

Expressions

Control flow and control structures

Subprograms

Basic input and output

Algorithm design techniques

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COMMENTS :

/** This is a JavaScript block comment.* Placement of the comment tokens on separate lines, and the use of* a vertical line of asterisks, is a convention that helps make the* comment more noticeable.*/

var x; // This is a JavaScript line comment.

DATA TYPES :Type Description_________________

Boolean A type capable of holding two values, False and True

Double A numeric data type capable of holding values between 4.94065645841247×10-324 and 1.79769313486232×10308 in absolute value, and zero

Long A numeric data type capable of holding integer values between 2147482648 and 2147483647, inclusive

String A type capable of holding strings, that is, ordered sequences of characters of essentially arbitrary length

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EXPRESSIONS : (example: arithmetic operators)

Operator Meaning

- Negation: the value of the right operand is negated.

* Multiplication: the values of the left and right operands are multiplied by one another.

/ Division: the value of the left operand is divided by the value of the right operand.

+ Addition: the values of the left and right operands are added together.

- Subtraction: the value of the right operand is subtracted from the value of the left operand.

var a = “Yeditepe ” + “University”

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CONTROL FLOW: how the current position in flowchart changes in time

1- sequence 2- alternatives 3- loops

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STRUCTURE COMPOSITION IN CONTROL FLOW

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PROGRAMMING LANGUAGES

Machine languages

Assembly languages

High-level languages

Application generators

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Machine Language

The only language that can be directly used by a computer

Consists of binary numbers that represent the instructions, memory locations and data necessary to solve a problem.

1- Operation code (opcode)

2- Operand

People aren’t very happy, accurate or efficient when writing 0s and 1s !

00000101 00001000

ADD 8

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Assembly Languages

Slightly higher than machine language

Consists of mnemonic symbols, easy-to-remember abbreviations

ADD, MUL, TOTAL rather than binary numbers

A special program called the ASSEMBLER translates the assembly language into the computer’s own machine code…

The program in the form it is written by a programmer = SOURCE CODE

After conversion into the machine language = OBJECT CODE

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High Level Languages

Resemble the human language or mathematical notation

Programmer needs to know less machine-specific details

Need to be also translated into machine language BUT…

… are MACHINE-INDEPENDENT or PORTABLE(can work in any computer with the applicable translator program)

COMPILERS = translate the high-level languages into machine-specific object code.

INTERPRETERS can also translate into object code, but one statement at a time

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FORTRAN (FORmulaTRANslator)

COBOL (COmmon Business Oriented Language)

BASIC (Beginners’ All-purpose Symbolic Instruction Code)

Pascal

C

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FORTRAN, with its mathematical orientation, efficient execution and numerical precision, is widely used in the scientific community to perform complex calculations.

Originally developed when punched cards were still the valid medium, FORTRAN has standard format of 80 characters per line.

SUBROUTINE = a sequence of statements, or module, that performs a particular processing task and can be called from various locations in the main program

FUNCTION = resembles a subroutine, but returns a single value tothe main program

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COBOL can handle input and output of large volumes of alphanumeric data, it is machine-independent, and has English-like syntax (self-documenting language).

BASIC’s most striking feature is its simplicity – can start writing programs within an hour of learning…It is often translated by interpreters.

BUT has slower running times and very inefficient !

Pascal was originally intended as a high-level language for teaching structured programming and top-down design.Very versatile and powerful, encourage relatively error-free programs and good programming habits.

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C was originally developed in Bell laboratories as part of the UNIX operating system.

It allows users to perform tasks that are normally achievable only by assembly languages.

C doesn’t divorce the programmer from the inner workings of a computer, therefore gives them great power.

It is the language of choice for programmers developing operating systems, compilers, and application software.

UNFORTUNATELY, it isn’t very user-friendly for beginners !