C# 4 and .NET 4

158 ❘ ChaPTer 7 OperAtOrs And cAsts
C# also supports conversions between different reference types and allows you to
defi ne how data types that you create behave when converted to and from other types.
Both of these topics are discussed later in this chapter.
Generics, on the other hand, allow you to avoid some of the most common situations
in which you would need to perform type conversions. See Chapter 5, “Generics” and
Chapter 10, “Collections,” for details.
Type Conversions
Often, you need to convert data from one type to another. Consider the following code:
byte value1 = 10;
byte value2 = 23;
byte total;
total = value1 + value2;
Console.WriteLine(total);
When you attempt to compile these lines, you get the following error message:
Cannot implicitly convert type ‘ int ’ to ‘ byte'
The problem here is that when you add 2 bytes together, the result will be returned as an int , not as
another byte . This is because a byte can contain only 8 bits of data, so adding 2 bytes together could very
easily result in a value that cannot be stored in a single byte . If you do want to store this result in a byte
variable, you are going to have to convert it back to a byte . The following sections discuss two conversion
mechanisms supported by C# — implicit and explicit.
implicit Conversions
Conversion between types can normally be achieved automatically (implicitly) only if you can guarantee
that the value is not changed in any way. This is why the previous code failed; by attempting a conversion
from an int to a byte , you were potentially losing 3 bytes of data. The compiler is not going to let you do
that unless you explicitly tell it that that ’ s what you want to do. If you store the result in a long instead of a
byte , however, you will have no problems:
byte value1 = 10;
byte value2 = 23;
long total;
total = value1 + value2;
Console.WriteLine(total);
// this will compile fine
Your program has compiled with no errors at this point because a long holds more bytes of data than
a byte , so there is no risk of data being lost. In these circumstances, the compiler is happy to make the
conversion for you, without your needing to ask for it explicitly.
The following table shows the implicit type conversions supported in C#:
from
sbyte
byte
short
ushort
int
uint
To
short, int, long, float, double, decimal, BigInteger
short, ushort, int, uint long, ulong, float, double, decimal,
BigInteger
int, long, float, double, decimal, BigInteger
int, uint, long, ulong, float, double, decimal, BigInteger
long, float double, decimal, BigInteger
long, ulong, float, double, decimal, BigInteger
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