int x = int.MaxValue;
In case of const variable it gives overflow error at compile time.
const int x = int.MaxValue;
const int y = int.MaxValue;
int z= x + y;
above statement will give compile time error of overflow in this condition if you want to bypass this error than use unchecked keyword.
int z = unchecked (x + y);
the above statement will not give any error.