Programming Languages

What You Will Learn About
What a programming language is
Machine language and assembly language
High-level programming languages
The shortcomings of early languages
Popular programming languages
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What You Will Learn About
The six phases of the program development life cycle (PDLC)
Why top-down programming makes programs easier to debug and maintain
The three basic types of control structures
Syntax errors and logic errors in programs
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Programming Languages
Programming languages are artificial languages created to tell the computer what to do
They consist of vocabulary and a set of rules to write programs
The program development life cycle (PDLC) is an organized method of software development
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Machine Language
Ada
Pascal
Fortran
COBOL
Assembly Language
Smalltalk
Visual Basic
BASIC
Java
C and C++

Development of Programming Languages
Programming languages are classified by levels or generations
Lower-level languages are the oldest
The five generations of programming languages are:
Machine languages
Assembly languages
Procedural languages
Problem-oriented languages
Natural languages
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First-Generation Languages
Machine language:
Consists of binary numbers (0s and 1s)
Is the earliest programming language
Is the only language the computer understands without translation
Is machine dependent
Each family of processors has its own machine language
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Second-Generation Languages
Assembly language:
Resembles machine language
Is a low-level language
Uses brief abbreviations for program instructions.
Abbreviations are called mnemonics
A program is written in source code (text file) and translated into machine language by an assembler
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Third-Generation Languages
Procedural languages:
Are high-level languages that tell the computer what to do and how to do it
Create programs at a high level of abstraction
Are easier to read, write, and maintain than machine and assembly languages
Use a compiler or interpreter to translate code
Fortran and COBOL are third-generation languages
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Compilers and Interpreters
A compiler is a program that changes source code to object code
An interpreter translates source code one line at a time and executes the instruction
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Third-Generation Languages (continued)
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Spaghetti Code and the Great Software Crisis:
GOTO statements resulted in programs that were difficult to follow
This problem led to the software crisis of the 1960s
Programs were not ready on time
Programs exceeded their budgets
Programs contained too many errors
Customers were not satisfied

Third-Generation Languages (continued)
Structured programming languages:
Were developed to improve software development
Include Algol and Pascal
Forbid the use of GOTO statements
Use control structures
IF-THEN-ELSE
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Third-Generation Languages (continued)
Modular programming languages:
Were developed because of problems in structured programming languages
Are used to create programs that are divided into separate modules
Each module carries out a special function
Require specified input to produce specified output
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Fourth-Generation Languages
Types of fourth-generation languages include:
Report generators
Languages for printing database reports
Query languages
Languages for getting information out of databases
Fourth-generation languages are nonprocedural
They do not force programmers to follow procedures to produce results
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Object-Oriented Programming
Object-oriented programming (OOP):
Relies on component reusability
The ability to produce program modules that perform a specific task
Eliminates the distinction between programs and data
Uses objects that contain data and procedures
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Objects
Objects are units of information that contain data as well as methods that process and manipulate the data
Classes of objects:
Hierarchy or category of objects
Objects at the top of the category are broader in scope than the subclass objects
Inheritance refers to an object’s capacity to “pass on” its characteristics to its subclasses
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Common Business-Oriented Language (COBOL)
COBOL:
The earliest (1959) high-level language
The most widely used business language
A proven way to do accounting, inventory, billing, and payroll
Requires programmers to explain what the program is doing at each step
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Sample Cobol program

Formula Translator (Fortran)
Fortran:
Began in the 1950s
Is suited to scientific, mathematical, and engineering applications
Is used to solve complex equations
Features simplicity, economy, and ease of use
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Sample Fortran program

Ada
Ada:
Named after Augusta Ada Byron
Incorporates modular programming
The required language for the U.S. Defense Department
Suitable for control of real-time systems (missiles)
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Sample Ada program

Beginner’s All-Purpose Symbolic
Instruction Code (BASIC)
BASIC:
An easy-to-use language available on personal computers
Widely taught in schools as a beginner’s programming language
Designed as an interpreted language
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Sample BASIC program

Visual Basic (VB)
Visual Basic:
Is widely used in program development packages
Uses event-driven programming
Enables the programmer to develop an application by using on-screen graphical user interfaces
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Sample Visual Basic

Pascal
Pascal:
Is named after Blaise Pascal
Encourages programmers to write well-structured programs
Widely accepted as a teaching language
Has been updated to reflect new approaches to programming
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Sample Pascal program

C
C:
Was developed by AT&T’s Bell Labs in the 1970s
Combines high-level programming language with assembly language
Programmers manipulate bits of data within a processing unit
Difficult to learn and programming is time consuming
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Sample C program

Smalltalk
Smalltalk:
Developed in the 1970s by Xerox Corp
“100% pure” object-oriented programming language
Not often chosen for software development
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Sample Smalltalk program

C++
C++:
Incorporates object-oriented features
Is widely used for professional program development
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Sample C++ program

Java
Java:
Developed by Sun Microsystems
An object-oriented, high-level programming language with a twist
First true cross-platform programming language
Gained acceptance faster than any other programming language
A simplified version of C++
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Java
Java, continued :
Java is designed to run on any computer platform
Java Virtual Machine enables cross-platform use
Java applets or small programs are downloaded to computers through networks
Weaknesses include:
The security risk in downloading applets
The speed in running the programs
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Sample Java Program
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Web-Based Languages
Markup languages:
Hypertext markup language (HTML) sets the attributes of text and objects within a Web page
Extensible markup language (XML) is used for sharing data and objects in a Web environment
Scripting languages:
VBScript is used to write short programs (scripts) that are embedded in Web pages
JavaScript is used to write scripts on Web pages
Visual Studio .NET:
Used for the development of scripts and programs that are accessible from the Web
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The Program Development Life Cycle (PDLC)
The PDLC was introduced in the 1970s to address problems in creating programs
It provides an organized plan for breaking down the task of program development into manageable parts
Six phases of the PDLC:
Defining the problem
Designing the program
Coding the program
Testing and debugging the program
Formalizing the solution
Implementing and maintaining the program
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Phase 1: Defining the Problem
The first step in program development
Systems analysts provide program specifications (specs) to programmers
Specs define:
Input data
Processing
Output
Appearance of user interface
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Phase 2: Designing the Program
Programmers create the program’s design
Top-down design focuses on the program’s main goal (main routine), then breaks the program into manageable components (subroutines/modules)
Control structures are used to see how each subroutine will do its job
Developing an algorithm is a step-by-step description of how to arrive at a solution
Program design tools:
Structure charts – show the top-down design
Flow charts – show the logic of program
Pseudo code – alternative to flow charts
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Structured Design
Control structures are logical constructs that specify how the instructions in a program are to be executed
Three types of control structures:
Sequence control structure – Instructions are executed in the order in which they appear
Selection control structures – The program branches to different instructions depending on whether a condition is met; IF…THEN…ELSE
Repetition control structure – The program repeats the same instructions over and over; DO-WHILE and DO-UNTIL
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Structure Chart and Flowchart
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Structure Chart
Flowchart

Phase 3: Coding the Program
Coding requires the translation of the algorithm into specific program instructions
An appropriate programming language is chosen, and the code is typed according to its syntax rules
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Phase 4: Testing and Debugging the Program
Testing and debugging eliminate all errors
Syntax and logic errors are corrected
Debugging is the process of eliminating errors
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Phase 5: Formalizing the Solution
Documentation is created for future use
The variable names and definitions, a description of the files needed, and the layout of the output are produced
A user manual is developed to explain how the program works
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Phase 6: Implementing and Maintaining
the Program
The program is:
Tested by users
Thoroughly documented
Maintained and evaluated regularly
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Summary
A programming language is an artificial language consisting of a vocabulary and a set of rules
Machine language is the lowest-level programming language
Assembly language contains symbols for programming instructions
Third-generation (high-level) languages require programmers to specify the procedures to be followed
Object-oriented languages combine procedures and data
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