Hi,
  i've recently been having trouble with my program which prompts for a
floating point number with scanf, and calculates some values from those
numbers. my problem is the fact that i want to be able to prompt the
input again if the user inputs something invalid (like a character or
something), or quit if the user types 'q'. the problem is, if i type a
'q' or anything besides a number when i prompts me, it skips the rest of
the scanf's! does anyone know why this could be happening? if so, please
help! thanks in advance.

victor dods

If it is expecting a number but receives a letter, it puts that letter back in
the "input queue", where it will find it next time you call scanf().

A better input method is to use fgets() to get a whole line (including the
'\n'), then you can check the input at your leisure, and convert it to a number
with sscanf() or other functions.

Peter Bennett VE7CEI                | Vessels shall be deemed to be in sight


TRIUMF, Vancouver, B.C., Canada     |                          ColRegs 3(k)
GPS and NMEA info and programs: ftp://sundae.triumf.ca/pub/peter/index.html
or: ftp://ftp-i2.informatik.rwth-aachen.de/pub/arnd/GPS/peter/index.html
or: http://vancouver-webpages.com/peter/index.html

Try either res = scanf (......); and then query the value of res (read up on the return value of
scanf)

Another choice is to flush the buffer after the scanf . Use flushall() or fflush().

A third choice would be to read each input charcters and translate to a floalting point number.  Use  
getche() or getchar() to read each character.  If q is entered, then exit, otherwise keep reading
digits and a period until you get a whitespace charcter (tab, return, space)

Good Luck

Sa'ad Raouf

  Hope this helps,

-- James

      A highly controversial study released today postulates a distant
      evolutionary relationship between bureaucrats and Homo Sapiens.

  A fourth (and very common) choice is to use fgets() to read a whole
line of user input, which the program can dissect at leisure. :-)  This
also happens to be the approach suggested in the FAQ.

/*   Indeed, C++ is a bit of an oddball of a language ... given the way that *
 * it requires private parts to be visible.  This increases the strength of  *
 * coupling dramatically...                       -- Dr. Rich Artym          */

: >
: > Hi,
: >   i've recently been having trouble with my program which prompts for a
: > floating point number with scanf, and calculates some values from those
: > numbers. my problem is the fact that i want to be able to prompt the
: > input again if the user inputs something invalid (like a character or
: > something), or quit if the user types 'q'. the problem is, if i type a
: > 'q' or anything besides a number when i prompts me, it skips the rest of
: > the scanf's! does anyone know why this could be happening? if so, please
: > help! thanks in advance.
: >
: > victor dodsThis has to do with the way that scanf is implemeneted.  scanf assumes that the data is correct and
: valid.  When the data is not valid, scanf will leave the charcters entered in the inputbuffer.  
: Subsequently, the next scanf statement will read what is in the input buffer.

: Try either res = scanf (......); and then query the value of res (read up on the return value of
: scanf)

: Another choice is to flush the buffer after the scanf . Use flushall() or fflush().

Before you give advice like the above you should make sure you know what
you are talking about. Quote from K&R >
"On an output stream, fflush causes any buffered but unwritten data to be
written; on an input stream, the effect is undefined"
Undefined means undefined, anything could happen thus you should not do it.
Also flushall() is an MSDOS specific function.
: A third choice would be to read each input charcters and translate to a floalting point number.  Use  
: getche() or getchar() to read each character.  If q is entered, then exit, otherwise keep reading
: digits and a period until you get a whitespace charcter (tab, return, space)

why not just use fgets() as getche() is MSDOS specific and Victor is
looking for a function that will read a newline terminated string.
You can pick the line read by fgets() apart with sscanf() afterwards.

gabor.
--
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No beast so fierce but knows some touch of pity
But I know none, And therefore am no beast
              Richard III., William Shakespeare


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