Checked and Unchecked (C# Reference)
C# statements can execute in either checked or unchecked context. In a checked context, arithmetic overflow raises an exception. In an unchecked context, arithmetic overflow is ignored and the result is truncated by discarding any high-order bits that don't fit in the destination type.
The following operations are affected by the overflow checking:
Expressions using the following predefined operators on integral types:
Explicit numeric conversions between integral types, or from
doubleto an integral type.
unchecked is specified, the default context for non-constant expressions (expressions that are evaluated at run time) is defined by the value of the -checked compiler option. By default the value of that option is unset and arithmetic operations are executed in an unchecked context.
For constant expressions (expressions that can be fully evaluated at compile time), the default context is always checked. Unless a constant expression is explicitly placed in an unchecked context, overflows that occur during the compile-time evaluation of the expression cause compile-time errors.