Answer 1

Hima

The answer is infact undefined, and depends on the compiler being used. Some compilers will result in 16 and 20, while others will produce 16 and 25.

When macro swaps the below expression is generates

(++x)*(++x)

The evaluation of the pre-increment operation ++x is where the undefined behavior in C comes in. With some compilers, the macro will reduce to (4)*(5), while in other cases, it will be evaluated as (5)*(5).

In this case the compiler last evaluated value 5 is assign to a and which is why the output is coming 25