While Loop Problem!!pls Help

[prasadkowli80]

hello friends...
In the C++ program below..there is something wrong in the While Loop. logic.What i want is that when we type
the letters --> y,Y,n or N then the program should exit.,else
it should not exit and then print as in the cout.
But the code is not working for me.it doesnt not exits even if when we enter --> y,Y,n or N.
Plss check the while loop and reply me with modifications

Thanx in advance
Prasad

Here is the code below:--

#include<iostream.h>
main()
{
char answer;
while ( (answer != 'y') || (answer != 'Y') || (answer != 'n') || (answer != 'N') ) //error checking for answer
{

cout << "Illegal character. Please enter again." ;
cin >> answer ;

} }

[sunburnt]

Here is one way to do it...

#include <iostream.h> 

main() 
{ 
	char answer; 
	do
	{
		cout << "Please enter a valid answer: ";
		cin >> answer;

	}while(answer != 'y' && answer != 'Y' && answer != 'n' && answer != 'N');
}

And here is another, more closely resembling yours.

#include <iostream.h> 

main() 
{ 
	char answer; 
	
	cout << "Enter answer: "
	cin >> answer;

	while(answer != 'y' && answer != 'Y' && answer != 'n' && answer != 'N')
	{
		cout << "Invalid answer, try again: ";
		cin >> answer;
	};

}

The problem was this line:
(answer != 'y') || (answer != 'Y') || (answer != 'n') || (answer != 'N')

This can be rewritten (according to D'morgan's law) as:

!(answer == 'y' && answer == 'Y' && answer == 'n' && answer == 'N')

which you can see is the exact opposite of what you want :-D

so either of these will work:
(answer != 'y' && answer != 'Y' && answer != 'n' && answer != 'N')

or

!((answer == 'y') || (answer == 'Y') || (answer == 'n') || (answer == 'N'))

Cheers.