Type conversions in C++ can occur between basic types like int to int, between basic and class types like int to a class, and between class types. There are four main situations: 1) Basic to basic uses implicit conversion rules. 2) Basic to class uses constructors, like converting an int to a time class. 3) Class to basic uses a user-defined conversion function in the class, like an overloaded typecast operator to convert a time class to an int. 4) Class to class can use a conversion function in the source class or a constructor in the destination class, like converting a dollar class to a rupee class.

1. Type Conversions
Different situations of data conversion between incompatible types
• 4 types of situation might arise in the data conversion:
– conversion from basic type to basic type
– Conversion from basic type to class type
– Conversion from class type to basic type
– Conversion from class type to class type
Type Conversion 1

2. basic type to class type
Constructors perform this type of conversions
int main()
{
int duration=85;
time t=duration;
t.display();
return 0;
}
Output:
1 hours 25 minutes
Type Conversion
class time
{
int hrs;
int mins;
public:
time()
{ }
time(int t)
{ hrs=t/60;
mins=t%60;
}
void display()
{cout<<hrs<<" hours";
cout<<mins<<" minutes";
}
};
2

3. class type to basic type
• constructor does not support this type of conversion
• So c++ allow us to define an overloaded casting operator that could be
used to convert a class type data to basic type.
• It is also known as conversion function
• Overloaded casting operator actually overloads the built in casting
operator.
• The casting operator function should satisfy following conditions
– It must be a class member
– It must not specify return type
– It must not have any arguments
3
Type Conversion

4. • Here typename is any basic data type.
• This overloaded typecast operator function does not have any return
type(not even void)
• Because the return type is the typename to which, the object is being
converted.
• Moreover it does not take any parameter
4
Type Conversion
• Syntax:-
operator typename()
{
…………
}
Example:
operator double()
{
……..
}
operator int()
{
………..
}
Cont…

5. class type to basic type
class time
{ int hrs;
int mins;
public:
time(int h,int m)
{hrs=h;
mins=m;
}
void display()
{ cout<<hrs<<" hours";
cout<<mins<<" minutes";
}
operator int()
{
return hrs*60+mins;
}
};
int main()
{
int duration;
time t(3,20);
t.display();
duration=t;
cout<<"duration:"<<duration<<" minutes";
return 0;
}
Output:
3 hours20 minutes
duration:200 minutes
5
Type Conversion

6. class type to class type
1. Using conversion function in source class
2. Using constructor in destination class
A objA;
B objB;
objA=objB;
6
Type Conversion
Destination
class Source class

7. class dollar
{
public:
int doll;
dollar(int x)
{
doll=x;
}
void show()
{
cout<<"Money dollars="<<doll<<endl;
}
};
class rupee
{ double rs;
public:
rupee(dollar d)
{
rs=d.doll*71.59;
}
void show()
{
cout<<"money in rupees:"<<rs;
}
};
int main()
{
dollar d1(5);
d1.show();
rupee r1=d1;
r1.show();
return 0;
}
Output:
Money dollars=5
money in rupees:357.95
7
Type Conversion
constructor in destination class

8. class rupee
{
public:
double rs;
rupee()
{ }
rupee(double rs)
{
this->rs=rs;
}
void show()
{
cout<<"money in rupees="<<rs;
}
};
class dollar
{
public:
int doll;
dollar(int x)
{
doll=x;
}
operator rupee()
{
return rupee(doll*71.59);
}
void show()
{
cout<<"Money in dollars="<<doll<<endl;
}
};
int main()
{
dollar d1(5);
d1.show();
rupee r1=d1;
r1.show();
return 0;
}
Output:
Money in dollars=5
money in rupees=357.95
8
Type Conversion
Using conversion function in source class