C Keywords and identifiers

C-Tutorial

C Introduction

C Keywords and identifiers

C Variables,constant and literals

C Datatype

C Input &Output (I/O)

C Operators

C if and if else Statements

C for loop

C while and do while loop

C break and continue

C switch statement

C goto statement

C functions

C user-defined functions

C Types of user-defined functions

C Recursion

C Storage class

C Arrays

C Pointers

C Pointers and Array

C Pointers and Function

C Memory allocation

C String

C String Functions

C Structure

C Structure and Pointers

C Structure and Function

C Union

C File input/output(I/O)

C Enumuration

C Preprocessor and Macros

C Standard library function

In this tutorial, you will learn about keywords; reserved words in C programming that are part of the syntax. Also, you will learn about identifiers and how to name them.

Character set

A character set is a set of alphabets, letters and some special characters that are valid in C language.

Alphabets

Uppercase: A B C ................................... X Y Z
Lowercase: a b c ...................................... x y z

C accepts both lowercase and uppercase alphabets as variables and functions.

Digits

0 1 2 3 4 5 6 7 8 9

Special Characters

,	<	>	.	_
(	)	;	$	:
%	[	]	#	?
‘	&	{	}	“
^	!	*	/	|
–	\	~	+

White space Characters

Blank space, newline, horizontal tab, carriage, return and form feed.

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C Keywords

Keywords are predefined, reserved words used in programming that have special meanings to the compiler. Keywords are part of the syntax and they cannot be used as an identifier. For example:

int money;

Here, int is a keyword that indicates money is a variable of type int (integer).

As C is a case sensitive language, all keywords must be written in lowercase. Here is a list of all keywords allowed in ANSI C.

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

All these keywords, their syntax, and application will be discussed in their respective topics. However, if you want a brief overview of these keywords without going further, visit List of all keywords in C programming.

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C Identifiers

Identifier refers to name given to entities such as variables, functions, structures etc.

Identifiers must be unique. They are created to give a unique name to an entity to identify it during the execution of the program. For example:

int money;
double accountBalance;

Here, money and accountBalance are identifiers.

Also remember, identifier names must be different from keywords. You cannot use int as an identifier because int is a keyword.

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Rules for naming identifiers

1. A valid identifier can have letters (both uppercase and lowercase letters), digits and underscores.
2. The first letter of an identifier should be either a letter or an underscore.
3. You cannot use keywords as identifiers.
4. There is no rule on how long an identifier can be. However, you may run into problems in some compilers if the identifier is longer than 31 characters.

You can choose any name as an identifier if you follow the above rule, however, give meaningful names to identifiers that make sense. 

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C Variables,constant and literals

C-Tutorial

C Introduction

C Keywords and identifiers

C Variables,constant and literals

C Datatype

C Input &Output (I/O)

C Operators

C if and if else Statements

C for loop

C while and do while loop

C break and continue

C switch statement

C goto statement

C functions

C user-defined functions

C Types of user-defined functions

C Recursion

C Storage class

C Arrays

C Pointers

C Pointers and Array

C Pointers and Function

C Memory allocation

C String

C String Functions

C Structure

C Structure and Pointers

C Structure and Function

C Union

C File input/output(I/O)

C Enumuration

C Preprocessor and Macros

C Standard library function

In this tutorial, you will learn about variables and rules for naming a variable. You will also learn about different literals in C

Variables

In programming, a variable is a container (storage area) to hold data.

To indicate the storage area, each variable should be given a unique name (identifier). Variable names are just the symbolic representation of a memory location. For example:

int playerScore = 95;

Here, playerScore is a variable of int type. Here, the variable is assigned an integer value 95.

The value of a variable can be changed, hence the name variable.

char ch = 'a';
// some code
ch = 'l';

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Rules for naming a variable

1. A variable name can only have letters (both uppercase and lowercase letters), digits and underscore.
2. The first letter of a variable should be either a letter or an underscore.
3. There is no rule on how long a variable name (identifier) can be. However, you may run into problems in some compilers if the variable name is longer than 31 characters.

Note: You should always try to give meaningful names to variables. For example: firstName is a better variable name than fn.

C is a strongly typed language. This means that the variable type cannot be changed once it is declared. For example:

int number = 5;      // integer variable
number = 5.5;        // error
double number;       // error

Here, the type of number variable is int. You cannot assign a floating-point (decimal) value 5.5 to this variable. Also, you cannot redefine the data type of the variable to double. By the way, to store the decimal values in C, you need to declare its type to either double or float.

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Literals

Literals are data used for representing fixed values. They can be used directly in the code. For example: 1, 2.5, ‘c’ etc.

Here, 1, 2.5 and ‘c’ are literals. Why? You cannot assign different values to these terms.

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1. Integers

An integer is a numeric literal(associated with numbers) without any fractional or exponential part. There are three types of integer literals in C programming:

• decimal (base 10)
• octal (base 8)
• hexadecimal (base 16)

For example:

Decimal: 0, -9, 22 etc
Octal: 021, 077, 033 etc
Hexadecimal: 0x7f, 0x2a, 0x521 etc

In C programming, octal starts with a 0, and hexadecimal starts with a 0x.

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2. Floating-point Literals

A floating-point literal is a numeric literal that has either a fractional form or an exponent form. For example:

-2.0
0.0000234
-0.22E-5

Note: E-5 = 10-5

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3. Characters

A character literal is created by enclosing a single character inside single quotation marks. For example: ‘a’, ‘m’, ‘F’, ‘2’, ‘}’ etc.

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4. Escape Sequences

Sometimes, it is necessary to use characters that cannot be typed or has special meaning in C programming. For example: newline(enter), tab, question mark etc.

In order to use these characters, escape sequences are used.

Escape Sequences	Character
\b	Backspace
\f	Form feed
\n	Newline
\r	Return
\t	Horizontal tab
\v	Vertical tab
\\	Backslash
\'	Single quotation mark
\"	Double quotation mark
\?	Question mark
\0	Null character

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For example: \n is used for a newline. The backslash \ causes escape from the normal way the characters are handled by the compiler.

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5. String Literals

A string literal is a sequence of characters enclosed in double-quote marks. For example:

"good"                  //string constant
""                     //null string constant
"      "               //string constant of six white space
"x"                    //string constant having a single character.
"Earth is round\n"         //prints string with a newline

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Constants

If you want to define a variable whose value cannot be changed, you can use the const keyword. This will create a constant. For example,

const double PI = 3.14;

Notice, we have added keyword const.

Here, PI is a symbolic constant; its value cannot be changed.

const double PI = 3.14;
PI = 2.9; //Error

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