Introduction to programming

you may already have used software,perhaps for word processing or spreadsheets,to solve problems.Perhaps now you are curious to learn how programmers develop software.As noted earlier,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 set of rules that provides a way of telling a computer hat operations to perform are called a programming language.There is not,just one programming language,there are many.

    Computer programming is an art.Many people believe that a programmer must be good at mathematics,have a memory for figures and technical information,and be prepared to spend many hours sitting at a computer,typing programs.However,given the right tools,and steps to follow,anyone can write well-designed programs.It is a task worth doing,as it is both stimulating and fulfilling.

WHAT PROGRAMMERS DO

In general the programmer's job is to convert problem solutions into instructions for the computer.That is,the programmer prepares the instructions of a computer program and runs those instructions on the computer,tests the program to see if it is working properly,and makes corrections to the program.The programmer also writes a report on the program.These activities are all done for the purpose of helping a user fill a need,such as paying employees,billing customers.

                             The programming activities just decribed could be done,perhaps,as solo activities.If a program is part of a system of several programs,the programmer ordinates with other programmers to make sure that the programs fit together well.

THE PROGRAMMING PROCESS

Developing a program involes steps similar to nay problem-solving task.There arefive main ingredients in the programming process.

1.Defining the Problem
2.Planning the Solution
3.Coding the Problem
4.Testing the Program
5.Documenting the program

1.Defining the Problem

         A programmer needs to meet with users from the client organization to analyze the problem,or meet with a system analyst who outlines the project.specifically,the task of defining the problem consists of identifying what is known and what is wanted to obtain.Eventually,the programmer produces a written agreement that,among other things,specifies the kind of input,processing and output required.

2.Planning the Solution

Two common ways of planning the solution to a problem are to draw flowcharts and to write pseudocode,or possibly both.Essentially,a flowchart is a pictorial representation of a step-by-step solution to a problem.It consists of arrows representing the direction the program takes and boxes and other symbols representing actions.

               Pseudocode is an English-like nonstandard language,which allows to state a solution with more precision than in plain English but with less precision than is required when using a formal programming language.

3.Coding the Problem

       As the programmer,the next step is to code the program-that is,to express a solution in a programming language.The programmer will translate the logic from the flowchart of pseudocode or some other tool to a programming language.There are many programming languages,BASIC,COBOL,Pascal,FORTRAN and C are some examples.

               Although programming languages operate grammatically,somewhat like the English language,they are much more precise.To get the program to work,the programmer has to follow exactly the rules,the syntax-of the language used.Of course,using the language correctly is no guarantee that the program will work.The point is that correct use of the language is the first step.The programmer will key the program and compose it,using a terminal or a personal computer.

4.Testing the Program

In theory,a well-designed program can be written correctly the first time.However,the imperfections of the world are still with us,so most programmers get used to the idea that their newly written programs probably have a few errors.Therefore,after coding the program,you must test it on the computer.This step involves these phases:

*Desk-checking:

        In desk checking,simply sit down and mentally trace or check ,the logic of the program to attempt to ensure that is is error-free and workable.Many organizations take this phase a step further with a walkthrough,a process in which a group of programmers-your peers-review your program and offer suggestions in a collegial way.

*Traslating:

A translator is a program that:

                     (1)Checks the syntax of the program to make sure the programming language was used correctly,giving all the syntax-error messages,called diagnostics,and then.

                           (2)Translates the program into a form the computer can understand.The mistakes are called syntax errors.The translator produces descriptive error messages.Programs are most commonly translated by a compiler,which translates your entire program at one time.The translation involves the original program,called a source module,which is transformed by a compiler into an object module. Pre-written programs from a system library may be added during the link/load phase,resulting in a load module,which can be executed by the computer.

*Debugging:
A term used extensively in programming.Debugging means detecting,locating,and correcting bugs(mistakes),usually by running the program.These bugs are logic errors,such as telling a computer to repeat an operation but not telling it how to stop repeating.


5.Documenting the program

An ongoing process,documentation is a detailed written description of the programming cycle and specific facts about the program.Typical program documentation materials include the origin and nature of the problem,a brief narrative description of the program,logic tools such as flowcharts and pseudocode,data-record descriptions,program listings,and testing results.Comments in the program itself are also considered as essential part of documentation.Many programmers document as they code.In a broader sense,program documentation can be part of the documentation for an entire system.

DEFINING THE PROBLEM

Before the actual process of coding,the program design which is a crucial step in program development needs to be done.

 The starting point for the design of any computer program must be a proper specification of its intended behavior.The behavior pattern is generally described in terms of inputs and outputs.Then the programmer designs a process(algorithm)which will derive tte outputs from the given inputs.In addition to these descriptions of inputs and outputs a program specification may include any constraints which must apply to the solution.

   These may include details of run time or space limitations,available equipment and utilities,as well as project deadlines.

          within a program specification,the definition of the inputs and outputs must include a description of their meaning,so that the programmer can understand the realtionship between them.

    A program needs t obe fully  specified,because it is part of a larger system and its design must be consistent with the methods used overall.Ina  commercial environment the specfication would come from a systems analyst,or systems manager,who studies user requirenments and is responsible for the design and co-ordination of a software project.The analyst hands over the specifications to a team of programmers,each of whom works on a set of programs.

               A commercial system is designed to meet the needs of the customer who will be its ultimate user.The outputs and reports,the screen messages and questions,and the inputs required-the user must understand all these and find them similar to those already in use.

 The users should therefore have as close a connection as possible with specifying the requirements.When they are satisfied,they will generally have to issue a formal acceptance" of the specification,by signing relevant documents.Because the programmers may not get a  chance to interact with the users themselves.they must be able to understand the specifications and follow them rigidly.Any improvements,which they would like to suggest,should be raised at he appropriate meetings.Moreover, because he is a part of a team,the programmer must document his programs in a predetermined way,so that the rest of the team can easily understand them.

THE SCOPE OF THE SPECIFICATION

              Most of the programs written today form part of much larger systems.To help a programmer understand a particular program's signification,its position in the entire system should be clear.Since an overall systems specification should be known before individual programs are specified,all the programmer needs to do is study the documentation.He should find among other things an  overall system description in diagramatic form.this may take the form of a system run chart,showing all files and programs involved-or it may be a data flow diagram,in which specific files are not mentioned.

The program gains a name according to the naming convention in use,also in addition to a  description of the program inputs and outputs in the form of detailed record formats,the programmer wil probably receive a description of the function of the program in some form.

PROGRAM PLANNING AND DESIGN

The popular methods used to describe the function of a program are pseudocode,structured charts and flow charts.
 Being Logical-the programmers often receives the program specification in pseudocode;there are a number of other ways to express problem logic.


Why Structure?

Structuring a programe helps to break it down into understandable chunks.Structured design cannot reduce the overall complexity of a system-but braking it down into smaller chunks(or modules)means that the amount of details that the programmer has to understand for any one module is much less than if dealing with the system as a  whole.

Modular Advantages:
1)Can reuse modules,which contain standard procedures throughout the program,saving development time.
2)The checking of conditions and errors situations are undivided in the modules,which contain the relevant coding-ensuring consistency and completeness.
3)Testing of individual modules,in isolation,makes tracing mistakes easier.
4)Amendments to single modules do not affect the rest of the program.
5)Library can be created for often-used routines,which are reliable and can go in other programs.
6)Modules can be named in such a way that they are easy to find in the the documentation,and be consistent.

from the Top Down

 The first stage in this process is to adopt the correct approach for developing the program from the information available.There are many tried and tested methods.The best known of these is the top down approach.    
            Using this ,look at the programme as a whole,then sub-divide it in to simpler components at lower levels,and repeat until no further breakdown is possible.The result is  a hierarchically distinct,manageable component,whose relationships and levels are clear and simple to see.
To describe the program at its highest level,universal program,then by a process of stepwise refinement,can be used.


The universal programme-Every working program contains a sequence of three modules

they are:
  1.The initialization of all parameters.
  2.The loop which forms the main body of the program
  3.The entire tidy up procedure.