Lecture 1

Reading: Textbook Chapter 1

Contents:

What is a program and why develop program?

What is a programming language?

Brief introduction of a system development life cycle

Steps in program development

Writing, editing, compiling and linking program

Program execution

What is a program?

• A program is a set of instructions for the computer to execute.

Why develop program?

• We develop program because we want to instruct the computer to do jobs for us.

What is a programming language?

• fig. 1-8

  

  • We use a programming language to write a computer program.
  • The only language understood directly by a computer is machine language, which consists of 0s and 1s only.
  • Every computer has its own set of machine language.
  • Symbolic languages: very similar to machine languages except that mnemonics are used to replace the numbers.
  • High-level languages: programming languages that are relatively easy to be understood by human.
  • High-level languages are portable to many different computers.
  • Today the most popular high-level language is C – the language to be learnt in this subject.
  • Symbolic languages and high-level languages must be translated into machine languages before they can be executed by the computer.
  • Research on using natural languages as programming languages is being done.

Brief introduction of a system development life cycle

fig. 1-11

• • Programming projects are built using a series of interrelated phases referred to as the system development life cycle.
  • Although the exact number and names of the phases differ depending on the environment, there is general agreement as to the steps that must be followed.
  • A life cycle model may have the following phases:

    Systems requirement: defines requirements that specify what the proposed system is to accomplish.

    Analysis: looks at different alternatives.

    Design: determines how the system will be built; functions of individual programs and the design of the files / databases is completed.

    Code: writing programs – focus of this subject.

    System test: all the programs are tested together to make sure the system works as a whole.

    Maintenance: keeps the system working once it has been put into production.

• • Phases may need to be reworked before entering the next phases.

Steps in program development

• • Understand the problem.
  • Develop the solution: tools include structure chart, pseudocode, and flowchart (using either pseudocode or flowchart will be sufficient).

fig. 1-12

• Structure chart: shows functional flow through the program; i.e. shows interaction between all the parts (modules) of the program.
  Pseudocode: part English, part program logic; describes the algorithm in detail and can be converted to a program easily.

fig. 1-13

• Write the program: converting the pseudocode or flowchart into programming language.
• Test the program: feed in sufficient test data to make sure that the program works in every case.

Writing, editing, compiling and linking program

fig. 1-9

• • The software that we use to write and edit our programs is the text editor.
  • A text editor lets you enter, change, and store character data.
  • The saved program file is called the source file.
  • A compiler is used to convert the source file into machine language.
  • The C compiler consists of the preprocessor and the translator.
  • The preprocessor scans for preprocessor directives which tell it to look for special code libraries, make substitutions in the program code, etc.
  • The translator converts the output of the preprocessor into machine language, the result being called object module.
  • The linker combines the program functions and the library functions into an executable program, which is ready to be run.

Program execution

fig. 1-10

• • To execute the program an operating system command is issued to load the program into primary memory and then execute it.
  • Typically, the program reads in data for processing, processes them, and generates the output; the program is then removed from memory.

- End of Lecture 1-