C Program Learning Part-2

Md. Mahmudun Nabi

CONSTANTS, VARIABLES AND DATA TYPES

CHARACTER SET

1. Letters

2. Digits

3. Special Characters

4. White Space

C TOKENS

In a passage of text, individual words and punctuation marks are called tokens. In C program the smallest individual units are known as C tokens. Six types of C tokens are used to write program and syntax of the language.

C TOKENS

Keywords - float, while

Constants - 15.5, 200

Special Symbols - {}, []

Identifiers - main, amount

Strings - “ABC”, “YEAR”

Operators - +, -, *, /

Keywords and Identifiers

Keywords

*Fixed meaning and can not be changed.

*Basic building block for program statement.

ANSI C Keyword

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

Identifiers

*Refers to the names of variables, functions and arrays.

*User defined names

*Consists of a sequence of letters and digits.

Rules for Identifiers

o First character must be an alphabet (or underscore).

o Consists of only letters, digits and underscore.

o Only first 31 characters are significant.

o Cannot be keyword.

o Must not contain white space.

Variables

*A variable is a data name that may be used to store data value

*A Constant remains unchanged during the execution of the program.

* A variables may take different values at different times during execution.

Conditions of Variables

o First character must be an alphabet (or underscore).

o Consists of only letters, digits and underscore.

o Only first 31 characters are significant.

o Cannot be keyword.

o Must not contain white space

o Uppercase and Lowercase are significant.

Data types

ANSI C supports three classes of data type:

1. Primary (or Fundamental) Data Type

2. Derived Data Type

3. User-defined Data Type

Primary Data Type
Signed	Range	Unsigned	Range
int or signed int (16 bit)	-32768 to 32767	unsigned int (16 bit)	0 to 65535
short int or signed short int (8 bit)	-128 to 127	unsigned int (8 bit)	0 to 255
long int or signed long int (32bit)	-214,74,83,648 to 214,74,83,647	unsigned long int (32 bit)	0 to 4294967295
float (32 bit)	3.4E-38 to 3.4E+38	double (64 bit)	1.7E-308 to 1.7E+308
long double (80 bit)	3.4E-4932 to 1.1E+4932
char or signed 1/2/2020 char (8 bit)	-128 to 127	unsigned char (8 bit)	0 to 255

Declaration of Variables

*Tell the compiler what the variable name is

*What type of data the variable will hold.

The Syntax for declaring a variable is as follows

data-type V1, V2 ,…….., Vn;

valid declarations are int count;

int number, total;

Assigning Values to Variables

Values can be assigned to variables using the assignment operator = as follows:

variable name = constant;

balance = 2000;

sum = 500;

Reading data from Keyboard

Giving values to variables is to input data through keyboard using the scanf function.

The general format of scanf is as follows:

scanf(“control string”, &variable1, &variable2,…….);

scanf(“%d”,&number); for integer type

scanf(“%f”,&number); for float type

scanf(“%c”,&name); for character type

OVERFLOW OF DATA

Problem of data overflow occurs when the value of a variable is either too big or too small for the data type to hold. When the addition result is bigger than the biggest number of bits can hold. For integer type overflow occurs when the variable exceeds the highest positive range value. Highest integer type variable value is 65535, when the value assigned to 65536 it occurs overflow.

UNDERFLOW OF DATA

When the value assigned to variable is less than the minimum allowable limit of an integer like -32768, integer underflow occurs.

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C Program Learning Part-2