operators in c++
in addition of the known operators, we have already seen two operators, namely, the insertion operator < < , and the extraction operator > > . other new operators are:
: : scope resolution operator
::* pointer-to-member declarator
-> * pointer-to-member operator
.* pointer-to-member operator
deleting memory release operator
endl line feed operator
new memory allocation operator
setw field width operator
in addition, c++ also allows us to provide new definitions to some of the built in operators. that is, we can give several meanings to an operator, depending upon the types of arguments used. this process is known as operator overloading.
scope resolution operator
c++ is a block-structured language. blocks and scopes can be used in constructing programs. we know that the same variables name can be used to have different meanings in different blocks. the scope of the variable extends from the point of its declaration till the end of the block containing the declaration. a variable declared inside a block is said to be local to that block. example:
…….
……
{
int x = 10
……….
………
}
………
………
{
int x = 1
……….
………
}
the two declaration of x refer to two different memory locations containing different values. another example:
……..
……..
{
int x = 10
…….
……
{
int x = 1
………. block2 block1
………
}
………
}
block2 is contained in block1. none that a declaration in an inner block hides a declaration of the same variable in an outer block and therefore, each declaration of x causes it to refer to a different data object. within the inner block, the variable x will refer to the data object declared therein.
scope-resolution operator used to uncover a hidden variable. it takes the following form:
: : variable-name
this operator allows access to the global version of variable. program bellow illustrates this feature:
|
/////////////////////[ scope resolution operator]////////////////////
#include < iostream.h>
int m = 10 //global m
main( )
{
int m = 20 //m redeclared, local to main
{
int k = m
int m = 30 //m again, local to inner block
cout < < "we are in inner block to \n"
cout < < "k=" < < k < < "\n"
cout < < "m=" < < m < < "\n"
cout < < ": :m = " < < : :m < < "\n"
}
cout < < "\nwe are in outer block \n"
cout < < "m = " < < m < < "\n"
cout < < ": : m = " < < : :m < < "\n"
}
/////////////////////////< program 3.1 > /////////////////////////////
|
the output of the program would be:
we are in inner block
k = 20
m = 30
: : m = 10
we are in outer block
m = 20
: :m=10
memory management operators
the new operator can be used to create objects of any type. it takes the following form:
pointer-variable = new data-type
here, pointer-variable is a pointer of type data-type. the new operator allocates sufficient memory to hold a data object of type data-type and returns the address of the object. example:
int *p= new int
float *q = new float
when a data object is no longer needed, it is destroyed to release the memory space for reuse.
the general form of its use is
deleting pointer-variable
the pointer variable is the pointer that points to a data object created with new. example:
deleting p
deleting q
manipulators
manipulators are operators are used to format the data display. the most commonly used manipulators are endl and setw.
endl has same effect as using the newline character "\n". for example:
………
cout < < "m = " < < m < < endl
< < "n = " < < n < < endl
< < "p = " < < p < < endl
………
………
would cause the three lines of output.
|
m =
|
2
|
5
|
9
|
7
|
|
n =
|
1
|
4
|
|
|
|
p =
|
1
|
7
|
5
|
|
note that this form is not the ideal output. it should appear as follow:
m = 2597
n = 14
p = 175
here, the numbers are right justified. its is used as follows:
cout < < setw(5) < < sum < < endl
program bellow illustrates theuse of endl and setw:
|
//////////////////////////< use of manipulators > /////////////////////
#include < iostream.h>
#include < iomanip.h>
main ( )
{
int basic = 950, allowance = 95 , total = 1045
cout < < setw(10) < < "basic" < < setw(10)< < basic < < endl
< < setw(10) < < "allowance " < < setw(10)< < allowance< < endl
< < setw(10) < < "total" < < setw(10) < < total < < endl
}
//////////////////////////< program 3.2 > //////////////////////////////
|
output of this program is given below:
basic 950
allowance 95
total 1045
type cast operator
c++ permits explicit type conversion of variables or expressions using the type cast operator.
type-name (expression)
example:
average = sum/flout(i)
a type-name behaves as if it is a function for converting values to a designated type.
expressions and implicit conversions
· an expression is a combination of operators, constants and variables arranged as per the rules of the language.
· it may be also include function calls which return values.
· an expression may consist of one or more operands and zero or more operators to produce a value.
· expression may be of four types, constant expressions, integral expressions, float expressions and pointer expressions.
- constant expressions consist of only constant values. example:
15
20+5/2.0
x
- integral expressions are those which produce integer results after implementing all the automatic and explicit type conversion. example:
m
m*n-5
m- x
5+int(2.0)
when m and n are integer variables.
- float expressions are those which , after all conversions, produce floating-point results.
example:
x + y
x * y/10
5 + float(10)
10.75
where x and y are floating –point variables.
- pointer expressions produce address values. example:
& m
ptr
ptr++1
"xyz"
where m is variable and ptr is a pointer.
we can mix data types in expressions. for example:
m=5+2.75
whenever data types are mixed in an expression, c++ performs the conversions automatically. this process is known as implicit or automatic conversion.
operators overloading
overloading means assigning different meanings to an operation depending on the context. the number and type of operands decide the nature of operation to follow. example: the statement
cout < < 75.86
invokes the definition for displaying a double type value, and
cout < < "well done"
invokes the definition for displaying a char value.
we can define + operator to add two structures or objects.
question:
- what is the application of scope resolution operator : : in c++.
- write a program to print the following output using setw:
3. cast the following variables one to another:
long int x
float y
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