Chapter 3 semantic traps

3.5 NULL pointer is not equal to Null StringThe compiler ensures that the pointer converted from 0 is not equal to any valid pointer. When constant 0 is converted to a pointer, this pointer cannot be unreferenced. In other words, when we assign 0 to a pointer variable, we absolutely cannot attempt to use the content stored in the memory to which the Pointer Points.
3.6 boundary computing and asymmetric Boundary
3.7 In the C language, the Value Order has only four operators (&, || ,? :,) There is a specified order of value. A comma is used to evaluate the expression on the left, discard the value, and then evaluate the value on the right. For example, A> B, the compiler may evaluate A or B first.

The following program is incorrect, because the order of evaluation is not fixed: I = 0; while (I <n) Y [I] = x [I ++];
The address of Y [I] is uncertain.

3.9 integer overflow in the unsigned arithmetic operation, there is no so-called 'overflow ': All the unsigned operations are modeled by the Npower of 2, and N is the number of digits in the result. If one of the operands in the arithmetic operation is a signed integer and the other is an unsigned integer, the signed integer is converted to an unsigned integer and does not overflow.