Understanding Type Casting or Type Conversion in C#

Type casting: An Overview

Type Casting or Type Conversion is a mechanism to convert one data type value to another one. Type conversion is possible if both the data types are compatible to each other; otherwise, you will get an InvalidCastException. In this C# Tutorial, we will explore more about Typecasting which will include Implicit conversion vs Explicit conversion vs User-defined conversion, different types of type casting or type conversions, and last but not least What the Upcasting and Downcasting. First Let's see the difference between Implicit conversion, Explicit conversion, and User-defined conversion.

Implicit vs Explicit vs User-defined.

Different Types of Type Casting or Type Conversion

1. Implicit conversion

   Implicit conversion is being done automatically by the compiler and no data will be lost. It includes the conversion of a smaller data type to a larger data type and the conversion of derived classes to base class. This is a safe type of conversion. Let's elaborate on this in the real-world example in C# Compiler.

    using System;
   
   public class Program
   {
   	public static void Main()
   	{
   		int i = 444;
   		double d1 = i; // Implicit casting from int to double
   
   		int i1 = 55;
   		// automatic type conversion
   		long l = i1;
   		float f = l;
   		
   		char i2 = '0';
   		int d2 = i2;
   
   		
   		Console.WriteLine($"d1 = {d1}"); 
   		Console.WriteLine($"l = {l}"); 
   		Console.WriteLine($"f = {f}"); 
   		Console.WriteLine($"d2 = {d2}"); 
   	}
   }
       

   Try it Yourself >>

   Output

   d1 = 444
   l = 55
   f = 55
   d2 = 48

2. Explicit conversion

   Explicit conversion is being done by using a cast operator. It includes conversion of larger data type to smaller data type and conversion of base class to derived classes. In this conversion information might be lost or the conversion might not succeed for some reason. This is an unsafe type of conversion.

    using System;
   
   public class Program
   {
   	public static void Main()
   	{
   		long l = 2222;
   		int i = (int)l; 
   		double d = 143.78;
   		int i1 = (int)d;   
   		
   		double d1 = 342.78;
   		float f = (float)d1;
   		decimal dec = (decimal)d1;
   
   		
   		Console.WriteLine($"i = {i}"); 
   		Console.WriteLine($"i1 = {i1}"); 
   		Console.WriteLine($"f = {f}"); 
   		Console.WriteLine($"dec = {dec}"); 
   		
   	}
   }
   

   Try it Yourself >>

   Output

    i = 2222
   i1 = 143
   f = 342.78
   dec = 342.78
   

3. User-defined conversion

   User-defined conversion is performed by using special methods that you can define to enable explicit and implicit conversions. It includes conversion of class to struct or basic data type and struct to class or basic data type. Also, all conversion methods must be declared as static.

    class RationalNumber
   {
    int numerator;
    int denominator;
   
    public RationalNumber(int num, int den)
    {
    numerator = num;
    denominator = den;
    }
   
    public static implicit operator RationalNumber(int i)
    {
    // Rational Number equivalant of an int type has 1 as denominator
    RationalNumber rationalnum = new RationalNumber(i, 1);
    return rationalnum;
    }
   
    public static explicit operator float(RationalNumber r)
    {
    float result = ((float)r.numerator) / r.denominator;
    return result;
    }
   
   }
   class Program
   {
    static void Main(string[] args)
    {
    // Implicit Conversion from int to rational number 
    RationalNumber rational1 = 23;
   
    //Explicit Conversion from rational number to float
    RationalNumber rational2 = new RationalNumber(3, 2);
    float d = (float)rational2;
    }
   }   

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What is the Upcasting and Downcasting?

There are two more casting terms Upcasting and Downcasting. basically, these are parts of Implicit conversion and Explicit conversion.

Implicit conversion of derived classes to base classes is called Upcasting and Explicit conversion of base class to derived classes is called Downcasting.

 class Base
{
 public int num1 { get; set; }
}

class Derived : Base
{
 public int num2 { get; set; }
}

class Program
{
 static void Main(string[] args)
 {
 Derived d1 = new Derived();
 //Upcasting
 Base b1 = d1;

 Base b2 = new Base();
 //Downcasting
 Derived d2 = (Derived)b2; 
 }
}
    

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