File window character eating

I'm trying to get into Pascal and I'm having some trouble understanding the file window.
1/ I want to skip leading non-digits from an input stream and I have the following code

read (c);
while not c in ['0'..'9'] do read (c);

This isn't working, properly, I'm not processing all the characters it seems. I'm not sure how to rewrite that loop using the input window. I think I must need it because I think my read statement is going too far.

2/ I'm trying to use the file window to slip blanks, like so

while input^ <> ' ' do read (c);

This sometimes crashes. What am I doing wrong?

gumby119

Asked: 1999-01-18

Advertise Here

Pascal

1 Solution

LVL 4

davidmwilliamsCommented: 1999-01-18

1/ You're right, your input goes too far because when you stop reading, you've already given c the first digit of the number. You do need to use the file window as you suspected, like this -

while not (input^ in ['0' .. '9'] do
read (c);

2/ I expect your code crashes on empty files, or if the file is padded with blanks - because you will try to read past the end of the file.
Try this routine -

Finished := False;
repeat
if eof then
Finished := True
else if input^ = ' ' then
read (c)
else
Finished := True
until Finished;

This is a bit more complicated, but more robust !

Were these perhaps homework questions? They actually are examples from a Pascal book called 'Oh, Pascal' ! That takes me back to COMP101 ....

gumby119Author Commented: 1999-01-18

Great stuff, and so quick too

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Expand your skills with this month's free Premium course.

File window character eating

Join & Write a Comment Already a member? Login.

Featured Post