Consider this C code to swap two integers and these five statements:

void swap(int *px, int *py)
{
*px = *px - *py;...

Question

Consider this C code to swap two integers and these five statements:

void swap(int *px, int *py)
{
    *px = *px - *py;
    *py = *px + *py;
    *px = *py - *px;
}

S1: will generate a compilation error
S2: may generate a segmentation fault at runtime depending on the arguments passed
S3: correctly implements the swap procedure for all input pointers referring to integers stored in memory locations accessible to the process
S4: implements the swap procedure correctly for some but not all valid input pointers
S5: may add or subtract integers and pointers

A. S1
B. S2 and S3
C. S2 and S4
D. S2 and S5

Accepted Answer

C. S2 and S4 The swap function uses arithmetic (subtract/add) instead of a temporary variable to exchange two integers via pointers. The question asks which statements correctly describe its behavior. The arithmetic trick works only when px != py (i.e., the pointers are different); if both pointers point to the same variable, the result is zero, not a swap. Also, if null pointers are passed, a segmentation fault can occur.