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C# Type Casting

Type casting is the conversion of a value from one type to another type. A cast is written in parentheses before the value, like (int).

A cast makes division exact

Division of two ints gives a whole number, so 7 / 2 gives 3. The cast turns 7 into a double first, and the same division gives 3.5.

using System;

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine(7 / 2);
        Console.WriteLine((double) 7 / 2);
    }
}

A cast drops decimals

The cast turns 9.99 into an int. The decimal part drops away, and the result is 9.

using System;

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine((int) 9.99);
    }
}

Convert reads a string

Convert.ToInt32 turns the string "42" into the int 42. Adding 8 then gives a number sum, not joined text.

using System;

class Program
{
    static void Main(string[] args)
    {
        int number = Convert.ToInt32("42");
        Console.WriteLine(number + 8);
    }
}

Example

using System;

class Program
{
    static void Main(string[] args)
    {
        string text = "17";
        int number = Convert.ToInt32(text);
        double half = (double) number / 2;
        Console.WriteLine(number);
        Console.WriteLine(half);
    }
}

Key points

  • A cast in parentheses before a value converts that value.
  • A cast to double lets a division keep its decimal part.
  • A cast to int drops the decimal part of a value.
  • Convert.ToInt32 reads a whole number out of a string.

In this example, Convert.ToInt32 turns the string "17" into the int 17, and the first line prints 17. A cast then turns the number into a double for the division. The second line prints the half, 8.5.

Note

A cast changes the value for that one use. The original variable keeps its own value and type.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Programiz C# Compiler

Exercise

What does (int) 9.99 print?