Elements of ‘C’ programming language for SEE and NEB

 

Elements of ‘C’ programming

 language for SEE and NEB

Every language has some basic elements and rules to write program. These basic elements are character set, variable, data types, constants, keywords (reserved words), variable declaration, expressions, statements, etc.

 

Character Set

The character set consists of alphabet digit or special symbol used to represent information. Character set used in C are as follows:

Alphabets	Uppercase (i.e A,B, ……….Y,Z)  or Lowercase (i.e. a,b,…………y,z)
Digits	0,1,2,………….8,9
Special symbol	+, -, *, /, =, ( ), [ ], < >, ‘, “, !, #, %, &, _, |, ^, ~, \, ., ;, “, ?
White space characters	Blank space, new line, tab etc..

 

Token

In C program the smallest individual units are known as C tokens. Each and every alphabet and punctuation symbols are called tokens.  Compiler collects the valid character set to make sensible tokens. so, it be said that tokens are collection of different characters, symbols operator and punctuators.

C tokens are of six types. They are,

Keywords (eg: int, while),

Identifiers (eg: main, total),

Constants (eg: 10, 20),

Strings (eg: “total”, “hello”),

Special symbols (eg: (), {}),

Operators (eg: +, /,-,*)

 

Reserved Words/Keywords

Keywords are command or predefined words that have specific meanings i.e. all keywords have fixed meanings and these meanings cannot be changed. C program is case sensitive program. So the keyword should in small case. They are:

Auto	break	case	char
const	continue	default	do
double	else	enum	extern
Float	for	goto	If
Int	long	register	return
Short	signed	sizeof	static
struct	switch	typedef	union
unsigned	void	volatile	white

 

Identifiers:

Identifiers can be defined as the name of the variables, functions, array, structures etc.. created by the programmer.  Keywords can’t be used as identifiers because they have some special meanings and functions in the program.

Example: length, area, a, b, sum, etc.

Rules for naming identifiers:

• Identifiers are the combination of digits, alphabets and underscore.
• Keywords can’t used as identifier
• It is not case sensitive i.e. lower case (small letter) or upper case (capital letter) can be used as identifier. Both lower case and upper case has distinct meanings such as num and NUM are two different identifiers.
• Any characters, digits (except some special symbols such as #, . etc) can be used, but the first letter should be a character.
• The length of identifiers based on the compiler. In earlier compilers it was 8 characters, ANSI C allows 31 characters but in modern compilers it may be of any length.
•  It must be unique in a program.
• Blank spaces are not allowed.

The identifiers are generally given meaningful names. Some examples of valid identifiers name-

Value               a          net_pay           rec1                 _data               MARKS

Some example of invalid identifiers name are-

5bc:     First character of identifiers should be an alphabet or underscore

int :      int is a keyword

rec#:    # is a special character

avg no:   blank space is not allowed.

 

Comments

Comments are arbitrary text written by a programmer, which are placed between the character sets /* and */.  Comments are helpful for what purpose programming is? Comment lines are not executable statements and therefore any text between /* and */ is ignored by the compiler.

In C program, a programmer can introduce comments in two ways: single line comment and multiple line comments. Single line comment is indicated by // (double slashes) where as multiple line comments is enclosed within /* and */

Example

// Single line comment

./* This program calculates sum of two different numbers*/

Variable:

Variable is an identifier or name given to any memory location that is stored the data while the execution of the program.  This data storage place is identified by the variable name.

In C language the variable must be declared with its data type before using in the program.

Types of variable:

i. Numeric variable: The variable that stores numeric data only called numeric variable. The numeric data may be whole number or fractional number.

ii. String variable: The variable that store characters data only are called string variable. The string data may be single character or string.

Rules For Declaring variable:

Variable name	Example
1. It cannot start with number	2num
2. It can contain number else where	num2
3. It cannot contain any arithmetic operator	a+b*c
4. It cannot contain any punctuation marks	@#%!
5. It may contain or begin with an underscore	_height
6. It cannot contain a C keyword	While
7. It cannot contain a space	num ber
8. It can be of mixed case	NumBer

 

Syntax: data_type variable1, variable2……..;

Example1:

int a,b,c sum;

Example 2:

int a=20;

char choice;

choice=’A’;

 

Constant:

Constant are the values that remain unchanged during program execution. C constant can be classified into two components.

a) Primary constant:   Eg. Integer, real, character, and string

b) Secondary Constant: Eg. Array, pointer, union, structure, etc..

Primary constant:

Integer constant: An integer constant refers to a sequence of a positive or negative nondecimal number. Example: int a=10, int b=-5 etc.

Real constant: Numeric constant that contains decimal points are called real constant or floating point constant. Example: float a=10.7, float b= -5.3 etc.

The character constant: A constant that contains a single alphabet, a single digit, or a single special symbol enclosed within a single inverted comma is called a character constant. Example:  char 'n'

String Constant:  A string constant has zero, one, or more than one character. A string constant is enclosed within double quotes ("  "). At the end of the string, \0 is automatically placed by the compiler.  Example: char add ="dhangadhi"