Trinity PU College, Mysuru Computer Science
Chapter-8
DATA TYPES
Variable:
A variable is an object or element and it is allowed change during the execution of the
program.
Variable represents the name of the memory location.
Declaration of a variable:
The syntax for declaring a variable is:
datatype variable_name;
The variable_name is an identifier. These variables are used to denote constants, arrays,
function, structures, classes and files.
The variables are named storage location whose values can be manipulated during program
run.
Examples:
Some valid variables are:
Reg_no, marks, name, student1, dob;
Some invalid variables are:
Double - keyword cannot be name of the variable.
Total marks - empty spaces are not allowed between variables names
2student - variable name should be begin with an alphabet
?result - variable should begin with alphabet or underscore only.
Initializing a variable:
The syntax to initialize a variable is:
datatype variable_name = value;
Example: Let b be a variable declared of the type int. then
int b = 100;
There are two values associated with a variable known as lvaue and rvalue. It means, for
example, let p be a variable declared of the type int. then int p = 100;
Here, name of the variable is p values assigned to variable is 100 i.e., rvalue
memory address location is 2000 i.e., lvalue.
Lvalue is the location value. It holds the memory address location at which the data value is
stored.
Rvalue is the data value. It holds the value assigned to the variable by the programmer i.e.,
Rvalue of p = 100.
C++ compiler allows us to declare a variable at run time. This is dynamic initialization. They
can be initialized anywhere in the program before they are used. The access modifier ‘const’
prefixed along with the data type for a variable does not allow the value to be changed at all
throughout the program. const int a = 100;
Data Types: Data Types can be defined as the set of values which can be stored in a variable
along with the operations that can be performed on those values.
The main aim of C++ program is to manipulate data. C++ defines several types of data and
each type has unique characteristics. C++ data types can be classified as:
1. The fundamental data type (built-in data)
2. Derived Data type
3. User-defined data type
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Trinity PU College, Mysuru Computer Science
The simple or fundamental data types are the primary data types which are not composed of
any
other data types. The simple data types/fundamental data types include int, char, float, double
and void.
The int type: The int type is used to store integers. Integers are whole numbers without any
fractional parts. This includes number such as 1, 45 and -9 are integers.
The General form of an integer declaration is:
int variable_name;
Example: int a, b=5;
The char type: It is character data type to store any character from the basic character set.
Characters are enclosed in single quotation marks (‘). ‘A’, ‘a’, ‘b’, ‘9’, ‘+’ etc. are character
constants.
The general form of a character declaration is:
char variable_list;
Example: char alpha=’a’;
The float type: This represents the number with fractional part i.e., real numbers. The float
type is used to store real numbers. Float is allocated 4 bytes (32 bits) of memory space.
The general form of a float declaration is:
float variable_name;
Example: float a=5.5;
The double type:
The double and float are very similar. The float type allows you to store single precision
floating point numbers, while the double keyword allows you to store double precision
floating point numbers. Its size is typically 8 bytes of memory space.
The general form of a double declaration is:
double variable_list;
Example: double a = 5.5e-7; //a is equivalent to 5.5x10-7.
The void type: The void data type has no values and no operations.
In this declaration the main function does not return any value.
Example: void main ()
The bool type: The bool type has logical value true or false. The identifier true has the value
1, and the identifier false has the value 0.
The general form of a bool declaration is:
bool variable_name;
Example: bool legal_age=true;
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Trinity PU College, Mysuru Computer Science
The statement legal_age= (age>=21); assigns the value true if age is greater than or equal to
21 or else it returns the value false.
Derived data types
a) These data types are constructed using simple or fundamental data types.
b) This includes arrays, functions, pointers and references.
User defined data types
a) These data types are also constructed using simple or fundamental data types.
b) Some user defined data types include structure, union, class and enumerated.
Enumerated data type: AN enumeration is a user defined type consisting of a set of named
constants called enumerators. enum is a keyword that assigns values 0, 1, 2……
automatically.
This helps in providing an alternative means for creating symbolic constants.
The syntax for enum is as follows:
enum [tag] {enum – list}; //for definition for enumerated type
enumtaddeclarator; //for declaration of variable type tag
Example 1:
enum choice {very_bad, bad, satisfactory, good, very_good};
choice mychoice;
C++ enum type conversion rules:
These rules apply to C++ only. There is an implicit conversion from any enum type to int.
Suppose this type exists.
enum MyEnumType {ALPHA, BETA, GAMMA};
Then the following lines are legal
int i = BETA; //give i value of 1
int j = 3 + GAMMA //give j a value of 5.
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