Chapter 1: C language Introduction

In this chapter you will learn about:

1. Introduction to C Language.
2. Features of C language.
3. Disadvantages of C language.
4. C program structure.
5. C Comments.
6. Important header files.
7. C programming Rules.

Introduction to C Language:

1. C is a Procedural programming language. This means there will a series of statements inside a procedure (function) that needs to be carried out.
2. C was developed by Dennis Ritchie at Bell labs in 1973.
3. C11 is the latest stable version released in 2011 December. This is supported by all major C compilers.
4. Unix and Linux operating system is written using C language.
5. C is a middle level programming language.
6. Many other programming languages like Java, Go, C# have been heavily influenced by C.
7. C programming allows static and dynamic memory management.
8. During 1970 and 1980 many versions of C have been implemented. Hence in 1989 ANSI C was introduced and was later accepted by ISO in 1990.
9. All the C source file will be saved as .c file extension. Example “helloWorld.c”
10. All the C header file will be saved as .h file extension. Example “stdio.h”

Features of C language:

1. Robust
2. Portable
3. Fast
4. Simple and easy to learn
5. Extensible

Disadvantages of C language:

1. Not an object-oriented language.
2. Some code needs to be recompiled when running on a different machine.
3. No constructors and destructors
4. There is no runtime checking. An error is known only after execution of a c program.
5. There is no strict type checking. In C programming language we can send integer value for a float data type.
6. No data security is available.

C is able to access low-level memory of hardware. This helps a programmer to develop efficient code. Hence C language is called as a middle-level programming language.

C program structure:

A simple C program should contain following lines.

#include<stdio.h>

int main()

{
	printf("Hello World \n");
	return 0;
}

Program  Explanation:

The first line “#include” is called as pre-processor directive. “stdio.h” is called a header file. This header file has declarations about standard input and output functions.

Next line is “int main()“. main() is the starting point of any c program. There is a return type specifies “int”, that informs the compiler that the function returns a value is of type int.

Next is opening brace ‘{‘, indicating the starting of function main().

Next line is a “printf()” function. This is used to display the output to the standard console. Note that every statement inside a function has ended with a semicolon. This informs the compiler that the statement has ended. And semicolon is mandatory to terminate a statement.

Next is “return 0;“. This will return the program execution back to the called function. In this case compiler. In C, returning value 0 indicates the program completed without any issues.

Last line is closing brace ‘}‘, indicating the end of function main().

To compile a C program in Linux use the following command:

gcc hello.c –o hello.o

To run the executed program, use below command:

./hello.o

C Comments:

Comments provide effective ways of knowing the functionality of a function. It is always a good practice to include comments in the beginning of a function with a short description of what it does.

The part written inside comments will be ignored by the compiler and the comments will be stripped off while compiling the program.

C supports 2 types of comments:

1. Single line comment:

// This is a single line comment

2. Multiline comment:

/* This is

an example of

multiline comment

*/

Example for comments:

#include<stdio.h>

int main()

{

	int num = 1; // integer variable

	/* Multi line comment

	num = num + 1;

	Above code will not be executed,

	as it is in comment

	*/

	return 0;

}

Important header files.

stdio.h : Provides input, output functions like printf(), scanf().

conio.h : Console input and output, provides functions like clrscr(), getch().

alloc.h : Provides memory allocation functions like malloc(), calloc(), free().

math.h : Provides math related functions like abs(), squrt().

string.h : Provides string related functions like strcpy(), strcat().

assert.h : Provides macros like assert(int).

C programming Rules:

While writing any C program, we must follow below rules:

1. 1. Every program should have a main() to run and generate an output.
   2. All the statements should be terminated by a semicolon.
   3. If the programmer has written only semicolon in a line, then it is treated as an empty statement.

Ex:

;

1. All the function names, variable names should be written in lower case, Upper case is used for symbolic constants.
2. Every opening braces should have an closing braces.

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