http://kor.i2p/books/The%20C%20Programming%20Language%20by%20K&R/chapter5.html
This
character is also the value that is compared against '\0' to control
the loop. The net effect is that characters are copied from t to s , up and including the terminating '\0' . As the final abbreviation, observe that a comparison against '\0' is
redundant, since the question is merely whether the expression is zero.