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Program Development






Software designers create new programs by using special applications programs, often called utility programs or development programs. A programmer uses another type of program called a text editor to write the new program in a special notation called a programming language. With the text editor, the programmer creates a text file, which is an ordered list of instructions, also called the program source file. The individual instructions that make up the program source file are called source code. At this point, a special applications program translates the source code into machine language, or object code – a format that the operating system will recognize as a proper program and be able to execute.

Three types of applications programs translate from source code to object code: compilers, interpreters, and assemblers. The three operate differently and on different types of programming languages, but they serve the same purpose of translating from a programming language into machine language.

A compiler translates text files written in a high-level programming language – such as Fortran, C, or Pascal – from the source code to the object code all at once. This differs from the approach taken by interpreted languages such as BASIC, APL and LISP, in which a program is translated into object code statement by statement as each instruction is executed. The advantage to interpreted languages is that they can begin executing the program immediately instead of having to wait for all of the source code to be compiled. Changes can also be made to the program fairly quickly without having to wait for it to be compiled again. The disadvantage of interpreted languages is that they are slow to execute, since the entire program must be translated one instruction at a time, each time the program is run. On the other hand, compiled languages are compiled only once and thus can be executed by the computer much more quickly than interpreted languages. For this reason, compiled languages are more common and are almost always used in professional and scientific applications.

Another type of translator is the assembler, which is used for programs or parts of programs written in assembly language. Assembly language is another programming language, but it is much more similar to machine language than other types of high-level languages. In assembly language, a single statement can usually be translated into a single instruction of machine language. Today, assembly language is rarely used to write an entire program, but is instead most often used when the programmer needs to directly control some aspect of the computer’s function.

Programs are often written as a set of smaller pieces, with each piece representing some aspect of the overall application program. After each piece has been compiled separately, a program called a linker combines all of the translated pieces into a single executable program.

Programs seldom work correctly the firs time, so a program called a debugger is often used to help find problems called bugs. Debugging programs are usually detect an event in the executing program and point the programmer back to the origin of the event in the program code.

Recent programming systems, such as Java, use a combination of approaches to create and execute programs. A compiler takes a Java source program and translates it into an intermediate form. Such intermediate programs are then transferred over the Internet into computers where an interpreter program then executes the intermediate form as an application program.

 

Exercise 1. Complete the following sentences:

1. Software designers create new programs ….

2. A programmer uses another type of program called ….

3. The individual instructions that make up the program source file are called ….

4. The advantage to interpreted languages is that ….

5. Another type of translator is the assembler, which is used ….

6. Programs are often written as a set of smaller pieces, ….

7. Recent programming systems, such as ….

 

Exercise 2. Try and put several questions to the given text.

Assignments:

ü Give your definitions to the terms source code and object code.

ü Name the applications programs which translate source code into object code.

ü What is the purpose of functioning of the debugging programs?

ü What are the intermediate programs used for?

 

 






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