Introduction to C

Introduction to C

C is one of the most popular general-purpose programming languages. C language has been designed and developed by Dennis Ritchie at AT&T Bell Laboratories, USA, in 1972. Several important concepts of C are drawn from ‘Basic Combined Programming Language (BPCL)’ and ‘B’ language. Martin Richards developed BCPL in 1967. The impact of BCPL on C is observed indirectly through the language B, which was developed by Ken Thompson in 1970.  C has an extensive set of capabilities and is a true general-purpose programming language. As such, it can be used for creating simple, interactive programs or highly sophisticated and complex engineering and scientific programs, within the context of truly structured language.

Why Use C?

In today’s world of computer programming, there are many high-level languages to choose from, such as C, C++, Java, Python and Ruby. These are all excellent languages suited for most programming task. Even so, there are several reasons why C is at the top of the list:

i.         The C language is not tied to any particular operating system. It can be used to develop new operating system. Major parts of popular operating systems like Windows, UNIX, Linux is still written in C. This is because even today when it comes to performance (speed of execution) nothing beats C. Moreover, if one is to extend the operating system to work with new device one needs to write device driver program which are exclusively written in C.

ii.          C is the base of most high-level and Object Oriented Programming Language such as C++, Java, C# and Objective C and it is hard to learn C++ or Java directly without learning C. 

iii.            Mobile device and embedded system have limited amount of memory. Considering this constrains C is a very good choice for building operating system and programs for such device for its efficiency and faster execution.

iv.            At times one is required to very closely interact with the hardware device. Since C provides several language elements that make this interaction feasible without compromising the performance it is the preferred choice of the programmer.

v.          C is a structural language. Structured language facilitates the development of a variety of programs in small modules or blocks. It is easy for writing, testing, debugging and maintenance with structured programming.

vi.         C programs are efficient, fast and highly portable, i.e. C programs written on one computer can run on another with small or almost no modification.

vii.     C is a free-form language. Multiple statements can be on the same line or can continue over multiple lines. White spaces (i.e. tab space or space bar) are ignored.

As these features show, C is an excellent choice for your first programming language. In learning C, you are not only learning one of today’s most powerful and popular programming languages, but you are also preparing yourself for object-oriented programming.

C is a middle-level language

C is often called a middle-level computer language. This does not mean that C is less powerful, harder to use, or less developed than a high-level language nor does it imply that C has the cumbersome nature of assembly language. Rather, C is thought of as a middle-level language because it combines the best elements of high-level language with the control and flexibility of assembly languages. In C, one can develop a program first and execute fast. It reduces the gap between high-level and low-level language; that is why it is known as a middle-level language.

C is a case-sensitive language

C is a case-sensitive language means that compiler distinguishes uppercase and lowercase letters.  Thus, in C the word main, Main and MAIN represent three distinct and different names. For this reason we should type all names in the same case.

Structure of a C program

Basic structure of a C program contains the following sections:

i.  Preprocessor Statements: The preprocessor statements begin with # (pound) symbol and are also called preprocessor directive. These statements instruct the compiler to include C preprocessor such as header files and symbolic constants before compiling the program. It is optional means a C program may not contain any preprocessor statements, but generally every C program depends upon some header files for function definition used in the program and for this contains one or more preprocessor statements. Each header file has extension ‘.h’. Header files contain the definitions of C library functions.

ii.  Global Declaration: This section declares some variables that are used in more than one function. These variables are known as global variables and are declared outside any function including main ( ). Global variables can be accessed by all the used define function as well as main ( ) function. Global declaration is also optional and a C program may or may not contain this.

iii.  The main ( ) function: Each and every C program must contain main ( ) function. Every C program starts execution from main ( ) function. No C program is executed without main ( ) function. The main ( ) function should be written in small (lowercase) letters.

iv.  Braces: Every C program must have a pair of curly braces ({, }) and must start immediately after the closing parenthesis of main ( ) function. The left brace (opening brace) indicates the beginning of the definition of main ( ) function and right brace (closing brace) indicates the end of the main ( ) function. Between these two braces, the program should have declaration and executable statements. These braces can also be used to specify the beginning and ending of user-define function. These two braces can also be used in compound statements.

v.    Local Declaration: Some variables are declared inside a function and are called local variable. A local variable can only be accessed from a function where it is declared. This portion is optional for a C program.

vi.   Program Statements: These statements are building blocks of a program. They represent the instruction for the computer to perform any specific task (operation).This portion may contain one or more input output statements, arithmetic statements, decision statements, control statements or assignment statements. Each statement should be terminated with a semicolon.

vii.  User-define Function: The functions defined by the user (programmer) are called user-define function. These are subprograms and perform user specific task. They may be written before or after the main ( ) function and generally called within main ( ) function. Unlike main ( ) function user-define function is optional to the programmer.

viii. Comments: Comments are not necessary in a program. However, to make the program understandable programmer can insert comments in the program. Compiler does not compiler comments but it is useful for documentation. The clarity of the program can be amplified if it is properly documented.

Comments are statements that give us information about the program or logics of program. Comments can be single line or multiline. Single line comments starts with the delimiters ‘//’ and terminate with the end of the line. Multiline comments are to be placed between the delimiters ‘/*’ and ‘*/’. Multiline comments can be nested. Comments are not a part of executable statements and compiler does not execute comments. But, for enhancing the readability of the program programmer should use comments and a good programmer frequently do it.      

Advantages of C

i.                   C contains a powerful data definition. The data types supported are characters, alphanumeric, integers, long integers, floats and double. It also supports string manipulation in the form of character array.

ii.                 C supports a powerful set of operators.

iii.              It also supports powerful graphics programming and directly operates with hardware. Execution of the program is faster.

iv.              An assembly code can also inserted into C program.

v.                 C programs are highly portable on any type of OS platforms.

vi.              System programs such as compiles, operating systems and device driver can be developed in C. For example operating system UNIX is developed in C.

vii.            The C language has 32 keywords and about 145 library functions and near about 30 header files in ANSI C.

viii.         C works closely with machine and matches assembly language in many ways.

ix.              The programs written in C language are efficient, fast and easy to understand.

x.                 Another important advantage of C is its ability to extend itself. We can easily add our own functions in standard C library.

xi.              C language is a structured programming language. This makes user to think of a problem in terms of function modules or blocks. Collections of these modules make a complete program. This modular structure makes program debugging, testing and maintenance easier.