Help! what's wrong with this program

[bbmmzz]

Here is my program:
int main()
{
int ival;

while(cin >ival, !cin.eof())
{
if(cin.bad())
return 0;
if(cin.fail())
{
cerr << "retry!" << endl;
cin.clear();
continue;
}
cout << ival << endl;
}
return 0;
}

Input int number, the program work well. But if input char, example
'a', it display "retry!" endless.
"cin >ival" is skip after input 'a'? Why?

[Obnoxious User]

Re: Help! what's wrong with this program

On Mon, 06 Oct 2008 08:25:06 -0700, bbmmzz wrote:

Here is my program:
int main()
{
int ival;
>
while(cin >ival, !cin.eof())
{
if(cin.bad())
return 0;
if(cin.fail())
{
cerr << "retry!" << endl;
cin.clear();
continue;
}
cout << ival << endl;
}
return 0;
}
>
Input int number, the program work well. But if input char, example 'a',
it display "retry!" endless.
"cin >ival" is skip after input 'a'? Why?

Because the 'a' is still in the buffer of std::cin. You need to
remove it, otherwise it will try to read it again and again and
always fail.

See std::istream::i gnore().

--
OU
Remember 18th of June 2008, Democracy died that afternoon.

http://frapedia.se/wiki/Information_in_English

[asm23]

Re: Help! what's wrong with this program

bbmmzz wrote:

Here is my program:
int main()
{
int ival;
>
while(cin >ival, !cin.eof())
{
if(cin.bad())
return 0;
if(cin.fail())
{
cerr << "retry!" << endl;
cin.clear();
continue;
}
cout << ival << endl;
}
return 0;
}
>
Input int number, the program work well. But if input char, example
'a', it display "retry!" endless.
"cin >ival" is skip after input 'a'? Why?

int main()
{
int ival;

while(cin >ival&&!cin.eof ()) //CHANGE HERE!
{
if(cin.bad())
return 0;
if(cin.fail())
{
cerr << "retry!" << endl;
cin.clear();
continue;
}
cout << ival << endl;
}
return 0;
}

This will work OK! But I can't explained it why...

[bbmmzz]

Re: Help! what's wrong with this program

On 10ÔÂ7ÈÕ, ÉÏÎç12ʱ11·Ö, asm23 <asmwarr...@gma il.comwrote:

bbmmzz wrote:

Here is my program:
int main()
{
int ival;

>

while(cin >ival, !cin.eof())
{
if(cin.bad())
return 0;
if(cin.fail())
{
cerr << "retry!" << endl;
cin.clear();
continue;
}
cout << ival << endl;
}
return 0;
}

>

Input int number, the program work well. But if input char, example
'a', it display "retry!" endless.
"cin >ival" is skip after input 'a'? Why?

>
int main()
{
int ival;
>
while(cin >ival&&!cin.eof ()) //CHANGE HERE!
{
if(cin.bad())
return 0;
if(cin.fail())
{
cerr << "retry!" << endl;
cin.clear();
continue;
}
cout << ival << endl;
}
return 0;
>
}
>
This will work OK! But I can't explained it why...- Òþ²Ø±»ÒýÓÃÎÄ×Ö -
>
- ÏÔʾÒýÓõÄÎÄ×Ö -

Thanks for your suggestion. Your change make the program check the
state of cin after "cin >ival", and if fail it will exit while loop
and never let user retry. In my original program, the value of while
condition is dependon the expression "!cin.eof() ".

I follow Obnoxious User's suggestion and add "cin.ignore ()" after
"cin.clear( )", it works.

[James Kanze]

Re: Help! what's wrong with this program

On Oct 6, 5:25 pm, bbmmzz <bumanz...@gmai l.comwrote:

Here is my program:
int main()
{
int ival;

while(cin >ival, !cin.eof())

Could you please explain what this is supposed to do?
ios::eof() really doesn't have any usable meaning until you know
that an input has failed. It can return true even if the input
succeeds.

The standard idiom for a loop would be:

while ( std::cin >ival ) ...

If you really want to put the error handling in the loop (which
I'm not sure is a good idea), you can do something like:

while ( std::cin >ival || ! std::cin.eof() ) ...

(Note that in this case, you will only look at eof if the input
fails.)

{
if(cin.bad())
return 0;
if(cin.fail())
{
cerr << "retry!" << endl;
cin.clear();
continue;
}
cout << ival << endl;
}
return 0;
}

Input int number, the program work well. But if input char, example
'a', it display "retry!" endless.
"cin >ival" is skip after input 'a'? Why?

What did you do with the 'a'? I don't see where you extracted
it.

(Also, returning from the middle of a loop or using continue is
generally a sign of a poor program.)

--
James Kanze (GABI Software) email:james.kan ze@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

[Hendrik Schober]

Re: Help! what's wrong with this program

James Kanze wrote:

[...]
(Also, returning from the middle of a loop or using continue is
generally a sign of a poor program.)

While I can't remember having ever used 'continue', I
have no objections at all against returning from the
middle of a loop.

Schobi

[Obnoxious User]

Re: Help! what's wrong with this program

On Tue, 07 Oct 2008 04:26:31 -0700, James Kanze wrote:

(Also, returning from the middle of a loop or using continue is
generally a sign of a poor program.)

Of course, those dreaded continues. Wasn't there a
letter called "Continue statement considered harmful" ;)

--
OU
Remember 18th of June 2008, Democracy died that afternoon.

http://frapedia.se/wiki/Information_in_English