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File window character eating

Posted on 1999-01-18
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Last Modified: 2011-09-20
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?
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Question by:gumby119
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2 Comments
 
LVL 4

Accepted Solution

by:
davidmwilliams earned 800 total points
ID: 1217502
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 ....
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Author Comment

by:gumby119
ID: 1217503
Great stuff, and so quick too
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