C++ Type Conversion

 C++ allows us to convert data of one type to that of another. This is known as type conversion.

There are two types of type conversion in C++.

1. Implicit Conversion
2. Explicit Conversion (also known as Type Casting)

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Implicit Type Conversion

The type conversion that is done automatically done by the compiler is known as implicit type conversion. This type of conversion is also known as automatic conversion.

Let us look at two examples of implicit type conversion.

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Example 1: Conversion From int to double

// Working of implicit type-conversion

#include <iostream>
using namespace std;

int main() {
   // assigning an int value to num_int
   int num_int = 9;

   // declaring a double type variable
   double num_double;
 
   // implicit conversion
   // assigning int value to a double variable
   num_double = num_int;

   cout << "num_int = " << num_int << endl;
   cout << "num_double = " << num_double << endl;

   return 0;
}

Output

num_int = 9
num_double = 9

In the program, we have assigned an int data to a double variable.

num_double = num_int;

Here, the int value is automatically converted to double by the compiler before it is assigned to the num_double variable. This is an example of implicit type conversion.

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Example 2: Automatic Conversion from double to int

//Working of Implicit type-conversion

#include <iostream>
using namespace std;

int main() {

   int num_int;
   double num_double = 9.99;

   // implicit conversion
   // assigning a double value to an int variable
   num_int = num_double;

   cout << "num_int = " << num_int << endl;
   cout << "num_double = " << num_double << endl;

   return 0;
}

Output

num_int = 9
num_double = 9.99

In the program, we have assigned a double data to an int variable.

num_double = num_int;

Here, the double value is automatically converted to int by the compiler before it is assigned to the num_int variable. This is also an example of implicit type conversion.

Note: Since int cannot have a decimal part, the digits after the decimal point are truncated in the above example.

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Data Loss During Conversion (Narrowing Conversion)

As we have seen from the above example, conversion from one data type to another is prone to data loss. This happens when data of a larger type is converted to data of a smaller type.

Possible Data Loss During Type Conversion

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C++ Explicit Conversion

When the user manually changes data from one type to another, this is known as explicit conversion. This type of conversion is also known as type casting.

There are three major ways in which we can use explicit conversion in C++. They are:

1. C-style type casting (also known as cast notation)
2. Function notation (also known as old C++ style type casting)
3. Type conversion operators

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C-style Type CastingAs the name suggests, this type of casting is favored by the C programming language. It is also known as cast notation.

The syntax for this style is:

(data_type)expression;

For example,

// initializing int variable
int num_int = 26;

// declaring double variable
double num_double;

// converting from int to double
num_double = (double)num_int;

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Function-style Casting

We can also use the function like notation to cast data from one type to another.

The syntax for this style is:

data_type(expression);

For example,

// initializing int variable
int num_int = 26;

// declaring double variable
double num_double;

// converting from int to double
num_double = double(num_int);

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Example 3: Type Casting

#include <iostream>

using namespace std;

int main() {
    // initializing a double variable
    double num_double = 3.56;
    cout << "num_double = " << num_double << endl;

    // C-style conversion from double to int
    int num_int1 = (int)num_double;
    cout << "num_int1   = " << num_int1 << endl;

    // function-style conversion from double to int
    int num_int2 = int(num_double);
    cout << "num_int2   = " << num_int2 << endl;

    return 0;
}

Output

num_double = 3.56
num_int1   = 3
num_int2   = 3

We used both the C style type conversion and the function-style casting for type conversion and displayed the results. Since they perform the same task, both give us the same output.

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Type Conversion Operators

Besides these two type castings, C++ also has four operators for type conversion. They are known as type conversion operators. They are:

• static_cast
• dynamic_cast
• const_cast
• reinterpret_cast

We will learn about these casts in later tutorials.

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