The characters /* in positions one and two of a line that contains no other characters are treated as an end-of-file indication and raise the ENDFILE condition.
Note that the sequence of characters /* in a line is not an end-of-file indication when input is attached to a file instead of a terminal. For example:
cat input.txt | ./plipgm
or
./plipgm < input.txt
where a line containing only /* from the input.txt file is not an end-of-file indication.
When using a terminal, use the control-D key sequence to generate an end-of-file indication.