Consider the following C program: #include <stdio.h> int main() { int x[] =…

Concept

In pointer arithmetic, if y points to an array element, then *(y - a) reads the element a positions before y. By contrast, *y - a first reads *y and then subtracts the integer a.

Parentheses and the position of the dereference operator therefore determine whether subtraction acts on a pointer or on an integer value. An accumulator must be updated with the value produced in every loop iteration.

Application

Here y = x + 4, so y points to x[4] and *y remains 10. For a = 0, 1, 2, 3, 4, the expression (*y - a) - *(y - a) produces the following updates:

1. At a = 0: (10 - 0) - 10 = 0, so b becomes 0.

2. At a = 1: (10 - 1) - 8 = 1, so b becomes 1.

3. At a = 2: (10 - 2) - 6 = 2, so b becomes 3.

4. At a = 3: (10 - 3) - 4 = 3, so b becomes 6.

5. At a = 4: (10 - 4) - 2 = 4, so b becomes 10.

Cross-check

Since x[4 - a] = 10 - 2a, each increment is (10 - a) - (10 - 2a) = a. Therefore the total is 0 + 1 + 2 + 3 + 4 = 10, which agrees with the iteration trace. The program prints 10.