Type Conversions in C#

Praveen Kumar
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This article has been excerpted from book "Visual C# Programmer's Guide"

Conversion allows you to treat one type as another. For example, storing an integer value in a long variable constitutes conversion from integer to a long. C# supports limited implicit conversions as well as explicit conversions.

With implicit conversions, you pass a type to another type without losing any data. Conversion from short to long-or from int to long, in the case that follows-is an example of implicit conversion.

int num1 = 34;
long num2 = a;

Implicit conversion is only possible when you pass a small-range type to a big-range type. A long data type can hold short and int values with no problem, but the reverse is not true without risking data loss. Some of the implicit conversions are as follows:

From sbyte to short, int, long, float, double, or decimal.
From byte to short, ushort, int, uint, long, ulong, float, double, or decimal.
From short to int, long, float, double, or decimal.
From ushort to int, uint, long, ulong, float, double, or decimal.
From int to long, float, double, or decimal.
From uint to long, ulong, float, double, or decimal.
From long to float, double, or decimal.
From ulong to float, double, or decimal.
From char to ushort, int, uint, long, ulong, float, double, or decimal.
From float to double.

In explicit conversions, you must cast a type with another type to pass data between them. For example, conversion from long to int is handled explicitly, as follows:

long num1 = 3443;
int num2 = (int)a;

Some possible explicit conversions are as follows:

From sbyte to byte, ushort, uint, ulong, or char.
From byte to sbyte or char.
From short to sbyte, byte, ushort, uint, ulong, or char.
From ushort to sbyte, byte, short, or char.
From int to sbyte, byte, short, ushort, uint, ulong, or char.
From uint to sbyte, byte, short, ushort, int, or char.
From long to sbyte, byte, short, ushort, int, uint, ulong, or char.
From ulong to sbyte, byte, short, ushort, int, uint, long, or char.
From char to sbyte, byte, or short.
From float to sbyte, byte, short, ushort, int, uint, long, ulong, char, or decimal.
From double to sbyte, byte, short, ushort, int, uint, long, ulong, char, float, or decimal.
From decimal to sbyte, byte, short, ushort, int, uint, long, ulong, char, float, or double.

However, prudent testing is always advisable to determine whether a conversion will cause loss of data or the unexpected conversion of values.

Boxing and Unboxing

The term boxing describes the process of converting a value type into a reference type. The following conversion is an example of boxing, which is always an implicit conversion.

        int int1 = 34;
        Object obj = int1;

With the preceding example, you could output these variables:

        Console.WriteLine(int1.ToString());
        Console.WriteLine(obj.ToString());

The value of both int1 and obj is 34.

When unboxing (the reverse process of boxing), you convert a reference type to a value type, as in the following example.

        Object obj = 43;
        int i = (int)obj;

From the example, you can output these variables:

        Console.WriteLine(i.ToString());
        Console.WriteLine(obj.ToString());

Conclusion

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