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Join Date: Jul 2004
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Newbie Poster
infinite loop... i dunno whether this question has been ask before but i've try to search but didn't found. so i ask it here...
very simple... if i declare
int Z;
cin >> Z;
if I enter integer, it works fine but i enter character it's looping.
how to prevent it from looping when character was entered?
very simple... if i declare
int Z;
cin >> Z;
if I enter integer, it works fine but i enter character it's looping.
how to prevent it from looping when character was entered?
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Location: Lawn Guylen, NY
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It looks as if you are automatically assuming that Z is an integer, and then doing some math calculations with it. When it's not an integer, but it's treated as one, you could end up in some sorta loop further down in your program. It looks as if your best option here is to determine whether Z is an integer, and if it isn't, prompt the user again to re-enter a number. You might also try doing to force z to be treated as an integer.
Regardless ... there might be a built-in function (I'm not exactly sure) that determines whether a value isInt() but if not, you will need to write one yourself. You would look at the ASCII equivalent of the value and see if it is an integer range or a character range. I'm not exactly positive how this would be done or if there is a simpler way (basically because I don't have an ASCII chart handy right now.) Perhaps someone else can offer more assistance than I.
z=(int)(z);
Regardless ... there might be a built-in function (I'm not exactly sure) that determines whether a value isInt() but if not, you will need to write one yourself. You would look at the ASCII equivalent of the value and see if it is an integer range or a character range. I'm not exactly positive how this would be done or if there is a simpler way (basically because I don't have an ASCII chart handy right now.) Perhaps someone else can offer more assistance than I.
Dani the Computer Science Gal
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Originally Posted by lara_
i dunno whether this question has been ask before but i've try to search but didn't found. so i ask it here...
very simple... if i declare
int Z;
cin >> Z;
if I enter integer, it works fine but i enter character it's looping.
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Originally Posted by lara_
how to prevent it from looping when character was entered?
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Join Date: Jun 2004
Location: Marin, CA, USA
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Unprevaricator
As a side note, if you think your program has an infinite loop, use the compiler's optimizer switches. That way the infinite loop will run 2-4 times faster!
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>It looks as if you are automatically assuming that Z is an integer
That's a reasonable assumption seeing as how Z was declared as int.
>When it's not an integer, but it's treated as one, you could end up in some sorta loop further down in your program.
The problem is with cin. The >> operator of cin will figure out what type the object is and convert the data from the standard input stream to that type. If there's no conversion then cin will leave the unconverted data in the stream and enter a failure state. This is a common problem with loops like this:
If a letter is entered, this will be an infinite loop because cin will continue to fail on the invalid data in the stream. The solution is to remove the offending input and clear the stream or read all data as a string and parse it for error handling. The latter is easy and the former can be done (rather naively) like this:
>to force z to be treated as an integer.
It's too late at that point. The issue isn't with Z being treated as an integer, but with cin's >> operator returning a failure status.
>there might be a built-in function (I'm not exactly sure) that determines whether a value isInt()
Provided the value is a string, you can try to convert it to an integer with atoi (yuck) or strtol (better). If the conversion succeeds then it's an integer, otherwise not. But this is a moot point if you're trying to read and convert input with the same function call, such as scanf or cin's >> operator.
>You would look at the ASCII equivalent of the value and see if it is an integer range or a character range.
Or just use
Since the standard requires digits to have adjacent values regardless of the character set. Or better yet, include <cctype> and say
But that only handles one character. For numbers longer than a single digit you need a loop. Once again, the point is moot because cin will try to convert the input to an integer before you can get your hands on it. By then the damage has presumably already been done.
>That way the infinite loop will run 2-4 times faster!
Kind of like trying to optimize your idle system process, no?
That's a reasonable assumption seeing as how Z was declared as int.
>When it's not an integer, but it's treated as one, you could end up in some sorta loop further down in your program.
The problem is with cin. The >> operator of cin will figure out what type the object is and convert the data from the standard input stream to that type. If there's no conversion then cin will leave the unconverted data in the stream and enter a failure state. This is a common problem with loops like this:
int number; while ( cin>> number ) cout<< number <<endl;
#include <iostream>
using namespace std;
bool get_number ( int& number )
{
while ( !( cin>> number ) ) {
if ( cin.eof() )
return false;
else {
char ch;
cin.clear();
cout<<"Invalid input, please try again: ";
while ( cin.get ( ch ) && ch != '\n' )
;
}
}
return true;
}
int main()
{
int number;
while ( get_number ( number ) )
cout<< number <<endl;
}It's too late at that point. The issue isn't with Z being treated as an integer, but with cin's >> operator returning a failure status.
>there might be a built-in function (I'm not exactly sure) that determines whether a value isInt()
Provided the value is a string, you can try to convert it to an integer with atoi (yuck) or strtol (better). If the conversion succeeds then it's an integer, otherwise not. But this is a moot point if you're trying to read and convert input with the same function call, such as scanf or cin's >> operator.
>You would look at the ASCII equivalent of the value and see if it is an integer range or a character range.
Or just use
if ( Z >= '0' && Z <= '9' )
if ( std::isdigit ( Z ) )
>That way the infinite loop will run 2-4 times faster!
Kind of like trying to optimize your idle system process, no?
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