Introduction to C                         Chapter 1

Objectives of this chapter:

1. Introduction
• History and Background of the C Programming Language 
2. Virtues of the C Programming Language 
3. How to write Programs in C (Program Design Concepts)

1. Introduction

• A programming language which can be written as either high level or low level. 
• It is mainly used for writing operating systems, system programs, graphics applications, and games. 
• Offers flexible. Modular, and open-ended programming on most types of computers, from PCs to mainframes. 
• C was developed in accord with UNIX (which was written in C) in 1972 at AT&T's Bell Laboratories by Dennis Ritchie. 
• The C programming language evolved from BCPL through the B programming language. 

2. Virtues of C

a) Design Features

• it has modern control structures 
• three forms of loops for handling repetitive operations. 
• three structures from choosing alternative paths of action. 
• through its varios types of variables, arrays and other data structures, C can represent a wide range of information 
• C advocates the use of modules or subroutines (called functions in C). 
• C makes it simple for you to document your programs by incorporating explanatory statements. 
• C encourages the programmer to use sound programming techniques such as top-down planning, structured programming, and modular design. The result will be a more reliable and understandabke program. 

b) Efficiency

• C is an efficient programming language that allows you to say what you mean using fewer words. 
• The final code tends to be compact and executes faster. 

c) Portability

• C is a portable language, which means that C programs written on one computer system can be run with little or no modifications on other computer systems. 
• C is a leader in portability. C compilers are widely available for many systems, from 8-bit microprocessors to the mighty mainframes. 

d) Power and Flexibility

• The powerful UNIX operating system was written in C , so are many of the supporting programs found on UNIX systems, such as text editors, compilers and interpreters for other languages like FORTRAN, PASCAL, LISP, and BASIC. 
• C programs have been used to solve physics and engineering problems and even for animating movie sequences 
• C has some of the fine control usually associated with assembly language. For example, in C you are able to manipulate or change a variable's contents at the bit level. 

e) Programmer Orientation.

• C is oriented to toward programmer needs. 
• It gives access to hardware. It lets you manipulate individual bits in memory. 
• It has a rich selection of operators. 
• C is less strict. Many operations such as converting forms of data are simpler in C. 
• C has a large library of useful functions that are generally available on most C implementations. 

3. Writing Programs in C

a) Define the Program's Objectives

• start with a clear idea of what the program is supposed to do. 
• Think generally 
• thin in terms of what information is needed by the program, what calculations and manipulations the program must do, and output the program should generate. 

b) Design the Program.

• decide on how the program will go about its implementation. 
• What should the use interface be like? How should the program be organised? 
• Decide on how to represent the data, and what methods to use to perform the processing. 
• Use of design principles: step-wise refinement, structured programming, modular design, and algorithm. 

c) Write the Code.

• Translate program design into the C programming language. 
• Create a source code file which is your program in C using a text editor. 

d) Compile the Code.

• At this step the source code will be translated into executable program using a C compiler. 
• The compiler also checks whether your program is valid C, if it finds any errors, it reports them to you and no executable program is produced, 

e) Run the Program.

• by running the executable program produced by the compiler, you can test whether the program runs as expected. 

f) Test and Debug the Program.

• your program may run incorrectly, it may contain bugs or errors. 
• At this step, any bugs or errors are corrected, and we go back to step (d). 

g) Maintain and Modify the Program.

• when the program is implemented, users may demand for new features, or because a undetected bug has surfaced. So, the program may need to be adapted or corrected and re-tested again. 
• Program maintenance will be greatly simplified if proper documentation and design was used.