1. Review of program specifications 2. Program design 3. Coding 4. Testing 5. Finalizing documentation

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1 1.1 Computer Program A computer program is a detailed set of instructions that directs a computer to perform the tasks necessary to process data into information. These instructions, usually written by a computer programmer, can be coded in a variety of programming languages. To create programs that are correct and maintainable, programmers follow a process called program development. 1.2 Program Development Program development is the process of producing one or more programs to perform specific tasks on a computer Five Steps in Program Development The process of program development has evolved into a series of five steps that most experts agree should take place when any program is developed. 1. Review of program specifications 2. Program design 3. Coding 4. Testing 5. Finalizing documentation Although the process steps are shown sequentially, program development usually requires returning to previous steps to correct errors. Reviewing the Program Specifications The programmer reviews the specifications created by the systems analys during the system design phase. Program specifications can consist of data flow diagrams, system flowcharts, process specifications that indicate the action to be taken on the data, a data dictionary identifying the data elements that will be used, screen formats, report layouts and actual documents such as invoices or checks. These documents help the programmer understand the work that needs to be done by the program. Also, the programmer meets once or more with the user and the systems analyst who designed the system to understand the purpose of the program from the user s point of view. If the programmer believes some aspect of the design should be changed, such as a screen layout, he or she discusses it with the systems analyst of the user. If the change is agreed on, the written design specification is changed.

2 However, the programmer should not change the specified system without the agreement of the systems analyst and the user. If a change is authorized, it should be recorded in the system design. The systems analyst and the user through the system design have specified what is to be done. It is the programmer s job to determine how to do it. Large programming jobs are usually assigned to more than one programmer. In these situations, a good system design is essential so that each programmer can be given a logical portion of the system to be programmed. Program Design The programmer determines and documents the specific actions the computer will take to accomplish the desired tasks. During program design, a logical solution to the programming task is developed and documented. Determining the logic for a computer program can be an extremely complex task. To aid in program design and development, a method called structured program design is commonly used. Coding The programmer writes the actual program instructions. Programs are written in different languages, which each have particular rules on how to instruct the computer to perform specific tasks, such as read a record or multiply two numbers. If a program design is thorough, logical, and well-structured, the coding process is greatly simplified and can sometimes be a one-for-one translation of a design step into a program step. Today, program code or instructions are usually entered direct into the computer via a terminal and stored in a disk drive. Using this approach, the programmer can partially enter a program one at a time and finish entering it at a later time. Program instructions are added, deleted, and changed until the programmer believes that the program design has been fully translated into program instructions and the program is ready for testing. Testing The written programs are tested to make sure they perform as intended. A programmer can perform several types of tests depending on what needs to be diagnosed. Desk checking is the process of reading the program and mentally reviewing its logic. This is a simple process that can be performed even if the person did not make the program himself. This process can be compared to proofreading a letter before you send it. However, this process is not reliable in detecting errors that are not that obvious.

3 Syntax errors are violations of the grammar rules if the language in which the program was written. An example of a syntax error would be the program command READ being misspelled as RED. Syntax errors missed by the programmer during desk checking are identified by the computer when it decodes the program instructions. Logic testing is what most programmers think of when the term testing is used. During logic testing, the sequence of program instructions is tested to make sure it yields the correct result. Logic errors may be caused by a programming oversight or a design error. Usually, logic testing is performed with the use of a test data. This data should simulate the data that is expected to be entered or used in the program. This data should be developed by referring to the system design but it should also try to break the program by including data outside the range of data that will be entered during normal operations. To be able to obtain an independent and unbiased test of the program, test data and the review of test results should be the responsibility of someone other than the person who made the program. Debugging is the process of locating and correcting program errors, or bugs, found during testing. The term was coined when the failure of one of the first computers was traced to a moth that was stuck in the electric components of the computer. Finalizing Documentation Throughout the program development process the programmer documents, or writes explanatory information about the program. Documentation should be an going part of developing a program and should only be finalized (organized and brought together) after the program is successfully tested and read for implementation. Documentation developed during the programming process should also include a narrative description of the program, program design documents such as flowcharts or pseudocodes, program listings, and test results. Comments in the program itself are also an important part of program documentation. Documentation is valuable because it helps the next programmer who will be tasked to make changes to the program. Proper documentation can substantially reduce the amount of time the new programmer will have to spend gathering information about the program that he is about to edit. In this final step, documents produced during steps 1 through 4 are brought together and organized Program Maintenance Program maintenance includes all changes to a program once it is implemented and processing real transactions. Sometimes, maintenance is required to correct errors that were not found during the testing step. Other times, maintenance is required to make changes following the demand of the users.

4 1.3 Programming Language A programming language is a set of written words and symbols that allow the programmer r user to communicate with the computer. As with English, Spanish, Filipino, or other spoken languages, programming languages have rules that govern their use and these rules are what we call syntax Four Categories of Programming Languages There are hundreds of programming languages, each with its own syntax. Some languages were developed for specific computers and others because of their success, have been standardized and adapted to a wide range of computers. Programming languages can be classified into one of four categories: 1. Machine Language Machine language is the fundamental language of the computer s processor. Programs written in all other categories of languages are eventually converted into machine language before they are executed. Because the instruction set is unique for a particular processor, machine languages are different for computers that have different processors. The advantage of writing a program in machine language is that the programmer can control the computer directly and accomplish exactly what needs to be done. Disadvantages are that they take a long time to write and difficult to review if the programmer is trying to find an error. Because they are written for specific processors, machine languages are also called low-level languages. 2. Assembly Language To make it easier for programmers to remember the specific machine instruction codes, assembly languages were developed. An assembly language is similar to a machine language but uses abbreviations called mnemonics or symbolic operation code to represent the machine operation code. Allows symbolic addressing which means that a specific computer memory location can be referenced by a name or symbol such as TOTAL, instead of by its actual address as it would have to be referenced in machine language. Assembly language programs can also include macroinstructions that generate more than once machine language instruction. Assembly language is converted into machine language instructions bu a special program called an assembler.

5 Though assembly languages are easier to use than machine languages, these languages are still considered as a low-level language because they are so closely related to the specific design of the computer. 3. High Level Languages High level languages contains mathematical, rational, or logical operators which can be grouped together to form what appear to be sentences called program statements. High level languages are much easier to learn than machine or assembly languages. High level languages can run on different types of computers because its machine independent. High-level languages are translated in one of two ways: a. With a compiler A compiler converts an entire program into machine language that is usually stored on a disk for later execution. The program to be converted is called the source program and the machine language produced is called the object program or object code. Compilers check the program syntax, perform limited logic checking, and make sure that the data that is going to be used in comparisons or calculations such as discount rate, is properly defined somewhere in the program. An important feature of compilers is that they produce an error listing of all program statements that do not meet the program language rules. The listing helps the programmer make the necessary changes to debug or correct the program. Because machine language is unique to each processor, different computers require different compilers for the same language. Example: a mainframe, minicomputer, and a personal computer would each have different compilers that would each have different compilers that would translate the same source language program into the specific machine language for each computer. b. With an interpreter While a compiler translates an entire program, an interpreter translates one program stamen at a time and then executes the resulting machine language before translating the next program statement. When using an interpreter, each time he program is run, the source program is interpreted into machine language and executed. No object program is produced.

6 Interpreters are often used with personal computers that do not have the memory or computing power required by compilers. The advantage of interpreters is that the compiling process is not necessary before program changes can be tested. The disadvantage of interpreters is that interpreted programs do not run as fast as compiled programs because the translation to machine language occurs each time the program is run. 4. Fourth Generation Languages The evolution of computer languages is sometimes described in terms of generations with machine (first generation), assembly (second generation), and high-level languages (third generation). Each generation is offered significant improvements on usage terms and programming flexibility over the previous generation. Fourth generation languages are described as nonprocedural which means that the programmer does not specify the procedures to be used to accomplish a task as is done with lower procedural language generations. Instead of telling the computer how to do the task, the programmer tells the computer what is to be done usually by describing the desired output. Example: database query language The advantage of fourth generation languages is that they are results oriented and they can be used by users not familiar with programming. The disadvantage of fourth generation languages is that they do not provide as many processing options to the programmer as other language generations and they require more computer processing power than other language generations. However, most experts believe that their ease of use far outweighs these disadvantages and they predict that fourth generation languages will continue to be more widely used. An extension of fourth generation languages, sometimes referred to as the fifth generation, is a natural language. A natural language is a type of query language that allows the user to enter question as if he or she were speaking to another person. Example: A fourth generation query might be stated as: LIST SALESPERSON TOTALSALES BY REGION

7 A natural language version of the same query might be: TELL ME THE NAME OF EACH SALESPERSON AND THE TOTAL SALES FOR EACH REGION The natural language allows the user more flexibility in the structure of the query and can even ask the user a question if it does not understand what is meant by the initial query statement. A few natural languages are available today but they are not yet widely used. Table 1.1. Program Instruction for; machine language (printed in a hexadecimal form), assembly language, and a high-level language called C. Machine Language Assembly Language High-Level Language 9b df 46 0c 9b d9 c0 9b db 7e f2 9b d b d8 c9 9b d9 5e fc fild WORD PTR [bp+12];qty fld ST(0) fstp TBYTE PTR [bp-14] fld DWORD PTR [bp+4];price fmul ST(0),ST(1) fstp DWORD PTR [bp-4];gross gross = gty * price 9b d9 c0 9b dc 16 ac 00 9b dd d8 9b dd 7e f0 90 9b Ba 66 f1 93 9b dd c b d9 46 fc 9b dc 0e b4 00 9b de e9 9b d9 5e b Fld ST(0) fcom QWORD PTR $T20002 fstp ST(0) fstsw WORD PTR [bp-16] fwait mov ah,byte PTR [bp-15] sahf ffreest(0) jbe $l193 fld DWORD PTR [bp-4]; gross fmul QWORD PTR $T20003 fsub fstp DWORD PTR [pb+8];net fwait if (qty>ceiling) net = gross (gross * discount_rate); eb 0d 90 8b 46 fc 8b 56 fe a jmp SHORT $l194 nop $193 mov ax,word PTR [bp-4];gross mov dx,word PTR [bp-2]; mov WORD PTR [bp+8],az ;net mov WORD PTR [bp+10],dx $l194; Else net = gross;