C Programming/Tokens

Tokens

C Supports Six Types of Tokens:

1. Identifiers
2. Keywords
3. Constants
4. Strings
5. Operators
6. Special Symbols

Identifiers

Identifiers are names for entities in a C program, such as variables, arrays, functions, structures, unions and labels. An identifier can be composed only of uppercase, lowercase letters, underscore and digits, but should start only with an alphabet or an underscore.

Rules for Naming Identifiers:

1. An identifier can only have alphanumeric characters (a-z , A-Z , 0-9) (i.e. letters & digits) and underscore( _ ) symbol.
2. Identifier names must be unique
3. The first character must be an alphabet or underscore.
4. Cannot be keyword as identifiers.
5. Should not be of length more than 31 characters.
6. Must not contain white spaces.
7. Identifiers are case-sensitive.

Kinds of identifiers:

1. Internal
2. External

Keywords

auto	double	int	struct
break	else	long	switch
case	enum	register	typedef
char	extern	return	union
const	float	short	unsigned
continue	for	signed	void
default	goto	sizeof	volatile
do	if	static	while

Constant

A constant is an identifier whose value cannot be altered in a program. Constants in C are the fixed values that are used in a program, and its value remains the same during the entire execution of the program.

1. Constants are also called literals.
2. Constants can be any of the data types.
3. Best practice to define constants using only upper-case.

Strings

Strings are actually one-dimensional array of characters terminated by a null character '\0'. Thus a null-terminated string contains the characters that comprise the string followed by a null.

//main.c
#include <stdio.h>

int main()
{
    //char name[] = "World";
    char name[6] = {'W', 'o', 'r', 'l', 'd', '\0'};
    printf("Hello %s!\n", name);
    return 0;
}

Operators

An operator is a symbol that tells the compiler to perform specific mathematical or logical functions. C language is rich in built-in operators and provides the following types of operators:

1. Arithmetic Operators
2. Relational Operators
3. Logical Operators
4. Bitwise Operators
5. Assignment Operators
6. Misc Operators

Differentiate

Keywords vs Identifiers

Keyword	Identifier
Predefined-word	User-defined word
Must be written in lowercase only	Can written in lowercase and uppercase
Has fixed meaning	Must be meaningful in the program
Whose meaning has already been explained to the C compiler	Whose meaning not explained to the C compiler
Combination of alphabetic characters	Combination of alphanumeric characters
Used only for it intended purpose	Used for required purpose
Underscore character is not considered as a letter	Underscore character is considered as a letter