Type Conversion in C++

A type cast is basically a conversion from one type to another. There are two types of type conversion:

1. Implicit Type Conversion Also known as ‘automatic type conversion’.
   • Done by the compiler on its own, without any external trigger from the user.
   • Generally takes place when in an expression more than one data type is present. In such condition type conversion (type promotion) takes place to avoid lose of data.
   • All the data types of the variables are upgraded to the data type of the variable with largest data type.

     bool -> char -> short int -> int -> 
     
     unsigned int -> long -> unsigned -> 
     
     long long -> float -> double -> long double
     

   • It is possible for implicit conversions to lose information, signs can be lost (when signed is implicitly converted to unsigned), and overflow can occur (when long long is implicitly converted to float).

   Example of Type Implicit Conversion:

   // An example of implicit conversion
   
   #include <iostream>
   using namespace std;
   
   int main()
   {
       int x = 10; // integer x
       char y = 'a'; // character c
   
       // y implicitly converted to int. ASCII
       // value of 'a' is 97
       x = x + y;
   
       // x is implicitly converted to float
       float z = x + 1.0;
   
       cout << "x = " << x << endl
            << "y = " << y << endl
            << "z = " << z << endl;
   
       return 0;
   }
   Output:

   x = 107
   y = a
   z = 108
   

2. Explicit Type Conversion: This process is also called type casting and it is user-defined. Here the user can typecast the result to make it of a particular data type.

   In C++, it can be done by two ways:

   • Converting by assignment: This is done by explicitly defining the required type in front of the expression in parenthesis. This can be also considered as forceful casting.

     Syntax:

     (type) expression

     where type indicates the data type to which the final result is converted.

     Example:

     // C++ program to demonstrate
     // explicit type casting
     
     #include <iostream>
     using namespace std;
     
     int main()
     {
         double x = 1.2;
     
         // Explicit conversion from double to int
         int sum = (int)x + 1;
     
         cout << "Sum = " << sum;
     
         return 0;
     }
     Output:

     Sum = 2
     

   • Conversion using Cast operator: A Cast operator is an unary operator which forces one data type to be converted into another data type.
     C++ supports four types of casting:
     1. Static Cast
     2. Dynamic Cast
     3. Const Cast
     4. Reinterpret Cast

     Example:

     #include <iostream>
     using namespace std;
     int main()
     {
         float f = 3.5;
     
         // using cast operator
         int b = static_cast<int>(f);
     
         cout << b;
     }
     Output:

     3
     

Advantages of Type Conversion:

• This is done to take advantage of certain features of type hierarchies or type representations.
• It helps to compute expressions containing variables of different data types.