variables & constants

7/30/2019 Variables & Constants

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VARIABLES &

CONSTANTS

Programming With C++


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Rules For Writing Variables: First character of a variable name may be Letters or

underscores. i

CSE_5a

a_very_long_name_that_isnt_very_useful

fahrenheit

First character of a variable cannot be a digit.

5a_CSE is not valid!

Case sensitive

CSE_5a is different from cse_5a


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VARIABLES: A quantity whose value may change during

execution of the program is called variable.

A named area in the computer memory, intended to

contain values of a certain kind.

They contain the data your program works with.

They can be used to store data to be used

elsewhere in the program.

In short they are the only way to manipulate data.


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Variables in memory:

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int my_int = 5;

double my_double = 3.5;

3.5

my_int

my_double


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Variables in memory:

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Whenever we write the variable name (my_int), we ask to

read the value of that variable.

3.5

my_int

my_double


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Rules For Writing Variables:

Blank Spaces are not allowed in a variablename.

Special characters, such as arithmeticoperators,#,^ cannot be used in a variablename.

Reserved C words cannot be used as variablenames.

A variable name declared for one data type,cannot be used to declare another data type.


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Valid and invalid variable

names:

Variable name Valid/ Invalid Remarks

Ahmed Valid

perform Valid

double Invalid C reserve word

switch Invalid C reserve word

_large valid

marriam valid


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Valid and invalid variable

names:

int invalid C reserve word

FLOAT Valid Keyword float is

in lower case

3taq invalid Starts withnumeric value

unsigned invalid C reserve word

x-y invalidSpecial characters

not allowed

Taq ahd invalid Space is not allowed

char invalid C reserve word


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Data types in C

Classification of a particular typeof information.

The actual values used in a program are called

Data, there are four basic types of data mostly

used in C.

1. int Integer

2. float Real values

3. double Large real values

4. char Characters


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Data types in C

Char: a single byte character.

int : an integer number usually 2bytes.

float : a single precision real number usually4 bytes.

double: a double precision real numberusually 8 bytes.

char

int

float

double


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Various data types in C:

Type Size in bytes

int 16bits (2bytes)

long int 32bits (4bytes)

unsigned int 16bits (2 bytes)

unsigned long int 32bits (4bytes)

float 32bits (4bytes)

long float 64bits (8bytes)double 64bits (8bytes)

long double 80bits (10bytes)

char 8bits (1byte)


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Integer Type Data:

An integer is a whole number, i.e a number without

a fraction or decimal point. It may have a positive

or a negative value. For example 601, 250, -6 and

501 are integers. Depending upon the maximumand minimum values, there are four types of

integer type data in C. these are

1. int

2. long int3. unsigned int

4. unsigned long int


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The int: the range ofint data type depends uponthe computer system being used and it takes 2 to 4bytes.

In MS DOS, an integer type variable takes two bytesin the memory and the range of values stored is from

-32768 to 32767.

The maximum and minimum values for integer data

types are specified in integer.h header file.


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The long int:A long int type data takes fourbytes in memory. It can store integer values from

-2147483648 to 2147483648.

The unsigned int :Itcan store positive wholenumbers. It takes two bytes in memory. It can store

integer values from 0 to 65,535.

The long unsigned int :long unsigned inttype data takes 4 bytes in memory. It can store

integer values from 0 to 4294967295.


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Real Type Data:

Real numbers consist of an integer and a non

integer part. These are also called floating pointnumbers.

Data consisting of real numbers is called float typedata.

Depending upon the maximum and minimum

values, there are two types of real type data.

These are:1. float

2. double


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float type data:The float type data isrepresented in decimal or exponential form. It may

be signed or unsigned. For example 23.26, 16.21,

0.56, -9.87 are floating type data. The float type data takes 4 bytes in the memory and

it can store real values from 3.4*10^-38 to3.4*10^+38.

Values for float data types are specified in float.hheader file.


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double type data:The double type data is also areal type data. It is used to store large real values.

A double type variable takes 8 bytes in the memoryand it can store real values from 1.7*10^-308 to1.7*10^+308.

long double type data:are used to store verylarge real data values. A long double variable takes

10 bytes in the memory, and can store real valuesfrom 3.4*10^-4932 to 1.1*10^+4932.


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Character type data:

Character type data consists of alphabetic

characters, numeric digits and special characters.

A single character takes 8 bits or 1 byte in the

memory.

The values for character data types are specified in

integer.h header file.

Arithmetic operations can also be performed on char

type variables.


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Declaring variables in C:

Specifying the name & data type of avariable is called Declaration of the variable.

When a variable is declared, its value isundefined.

The syntax to declare a variable in C is:

type list of variables;

Example:double cm, inches;


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Type:specifies data type of variables. Forexample int is used to declare an integer typevariable and float is used to declare float type data.

List of variables: specifies a list of variablesseparated by commas. In a single statement more

than one variables of same data type can be

declared.


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Example: variable declarations

int i;

char c;

float f1, f2, f3;

float height;

double distance;

int xyz, a, b, c;


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Initialization of variables:

Assigning a known value to a variable at the

time of its declaration is called initializing of

the variable. For example to declare variables a, b, c of

integer type and assigning values a=10 and

b=60 the statements are written as:

int a=10, b=60, c;

float num = 67.3;


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Constants:

A quantity that cannot change its value

during execution of the program is called

constant.

There are two types of constants in C.

these are:

1. Literal Constant

2. Symbolic Constant


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Literal Constant:

A literal Constant is a value that is typed

directly in a program. It appears in the

program wherever it is needed.

There are four types of Literal Constants

are as follows:

1. Integer constants

2. Floating point constants3. Character constants

4. String constants


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Symbolic Constant: A symbolic constant is an identifier that represent a constant

value.

For example the value of(pi) is frequently used in engineeringcalculations. It represents a constant value approximately equal to

3.141593. instead of typing the numeric value each time, this valueis assigned to an identifier and that identifier is written wheneverthe value of(pi) is to be used. This identifier represents a constantvalue and is called Symbolic Constant.

There are two ways to declare symbolic constant. These are:

1. using the define directive

2. using the const qualifier


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define Directive:It is a preprocessor directive. It is used to assign a

constantquantity to an identifier. This directive canbe used anywhere in the program. its syntax is:

#define identifier constant

Example:#define Pi 3.141593f


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Identifier:specifiesthe identifiername towhich the constant

value is to be assigned.

Constant:specifies theconstant value that isto be assigned to the

identifier.

#define statement doesnot end with semicolon.

The identifier specified

in the define directive isnot variable & It doesnot have any data type.

It is a convention in Cto write identifiers in

capital letters, this isdone to distinguishthem from variables.


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const Qualifier: The const qualifier is used to define a variable with a

value that is fixed.

The value is assigned to the variable at the time of itsdeclaration.

In the following statement, pi has been declared as

floating point variable and a fixed value has been

assigned to it.const float pi = 3.141593f;

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