c# checked ,unchecked words

while doing a type casting .... there is chance of overflow or underflow .

byte a1 = 222;
byte a2= 212;
byte sum = checked((byte)Add(a1, a2));

chances are that we get bad value for sum ( 222+212-256)

we can tell compiler to be pricky about such happenings. (now you try and catch the overflow)
try
{
byte sum = checked((byte)Add(a1, a2));
//or you can write
//checked
//{
// byte sum = (byte)Add(a1, a2);
// Console.WriteLine("sum = {0}", sum);
//}
}
catch (OverflowException ex)
{
Console.WriteLine(ex.Message);
}

as reverse you can explicitly want to ignore as below..

unchecked
{
byte sum = (byte)(a1 + a2);
}

You will do the above when -- you already have a project wide setting Overflow