Answer:

The parentheses around the assignment expression (in red) are needed because assignment has lower precidence than !=.

while ( (ch = getchar()) != EOF ) 

Without the red parenthese, the statement would work as if it were written like this:

while ( ch = (getchar() != EOF) ) 

which would assign either a 0 (for false) or a 1 (for true) to ch.