05_Data Types_C progarmming

Character Set

Alphabets: a,b,c........z or A,B,C,….....Z or _  (underscore)

Digits:   0,1,2,3,4,….9

Special Symbol: !, $, &, @, #, ^, *.. etc

White spaces:  blank space, horizontal tab, new line.....

Comment

A comment is a text in the program which wont be compiled or executed.

Single line comment: It is written by using ; //....comment.....

//This is the comment which is no executed.

Multi-line comment: It is written by using '/*…....comment........*/'

C Tokens

The basic and smallest element used to develop the program and recognized by the c compiler is called c tokens.

There are five types of tokens which are:

1. Keywords: float, while, if....etc

2. Identifier: num, sum....etc

3. Constants: 1,2,3...etc

4. String Constants: "ABC", "Global IT"…..etc

5. Operators: +, -, *, /....etc

Keywords

Keywords is a reserved word that has standard and predefined meaning in C. It has already defined in C programming language.

The keywords cannot be used as variable names/ identifier because if we try to do so, then we are trying to assign a new meaning to the keyword, which is not allowed by the compiler.

There are 32 keywords in C:

  

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

Identifier

The identifier is the name given to various program

elements such as variable, function, label and an

other user-defined item.

There are 53 alphabetic character: 52 letters and

one is _ (underscore)

Rules:

Must consist of only letters, digits, or underscore

First letter must be alphabet or _

Only first 31 characters are significant

Keyword cannot be used as identifier

Must not contains white space.

Data Types

The data types is an instruction that is used to

declare the category or type of the variable being

used in the program. Any variable used in the program

must be declared before using

it.

Data types can be classified as:

Primary Data Types:

• int
• float
• char
• void

Derived Data Types:

• function
• array
• pointer

User-defined Data types:

• structure
• union

Primary Data Types

Primary Data Types, their size and range

 

Type	Size (bytes)	Range
Int or signed int	2	-32,768 to 32,767
Unsigned int	2	0 to 65535
Short  int or signed short int	1	-128 to 127
Unsigned short int	1	0 to 255
Long int or signed long int	4	-2,147,483,648 to 2,147,483,647
Unsigned long int	4	0 to 4,294,967,295
float	4	3.4E-38 to 3.4E+38
double	8	1.7E-308 to 1.7E+308
Long double	10	3.4E-4932 to 1.1E+4932
Char or signed char	1	-128 to 127
Unsigned char	1	0 to 255

Constant and Variable

A value that does not change during the execution

of the programs is called constants.

Variable is a symbolic name which is used to store

different types of the data in the computer memory

and may change during the program execution.

Variable Declaration

Syntax:

int num;

Variable Initilization

Syntax:

int num=10;

Local Variable and Global Variable

Local Variable	Global Variable
It is declared inside a function	It is declared outside the function
If it is not initilized, a garbage value is stored	If it is not initilized zero is stored as default.
Data of the local variable can be accessed by only one function.	Data of the global variable can be accessed by multiple functions.
It is stored on the stack unless specified.	It is stored on a fixed location decided by the compiler.
e.g. #include<stdio.h> int main() { int num; return 0; }	e.g. #include<stdio.h> int num; int main() { return 0; }

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