C# statements executes 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.
short m = 32767; short n = 32767; int result1 = checked((short)(m + n)); //will throw an OverflowException int result2 = unchecked((short)(m + n)); // will return -2
If neither of these are specified then the default context will rely on other factors, such as compiler options.