C# Language Specification

Conversions

A conversion enables an expression to be treated as being of a particular type. A conversion may cause an expression of a given type to be treated as having a different type, or it may cause an expression without a type to get a type. Conversions can be implicit or explicit, and this determines whether an explicit cast is required. For instance, the conversion from type int to type long is implicit, so expressions of type int can implicitly be treated as type long. The opposite conversion, from type long to type int, is explicit and so an explicit cast is required.

int a = 123;

long b = a; // implicit conversion from int to long
int c = (int) b; // explicit conversion from long to int

Some conversions are defined by the language. Programs may also define their own conversions (§6.4).

1.