Need to add a loop to exit or repeat in C++ - c++

Question

I want to make a code that asks user for input either to quit or repeat. I am not getting the desired output.
int main()
{
char yes,yn;
do
{
cout << "Hello world!" << endl;
while(yn != 'y' || yn != 'Y' || yn != 'n' || yn != 'N')
{
cout<<"enter (Y/N): ";
cin>>yes;
yn = yes;
}
}while(yn == 'y' || yn == 'Y');
}
Program asks for user input, when I input "Y,y,N or n", it should get out of the loop and then decide whether exit or repeat. But it isn't getting out of the loop and asking me for input again and again. I am not getting what is stopping to get out of the loop.

Answer 1

I didn't test, but your issue seems to be here:
while(yn != 'y' || yn != 'Y' || yn != 'n' || yn != 'N')
This condition is always true (yet shouldn't). It should be :
while(yn != 'y' && yn != 'Y' && yn != 'n' && yn != 'N')
or
while(!(yn == 'y' || yn == 'Y' || yn == 'n' || yn == 'N'))
Moreover, yn isn't initiliazed, you may want to do a do { ... } while(...); again.

Answer 2

while(yn != 'y' || yn != 'Y' || yn != 'n' || yn != 'N')
Is always true. It should be
while(yn != 'y' && yn != 'Y' && yn != 'n' && yn != 'N')

Answer 3

Firstly, this expression:
(yn != 'y' || yn != 'Y' || yn != 'n' || yn != 'N')
is always true, as yn is always not equal to one of those things.
(yn != 'y' && yn != 'Y' && yn != 'n' && yn != 'N')
is probably what you meant.
Secondly, your life would be easier if you did
yes = toupper (yes);
(i.e. put it in upper case), then you'd only have to look for one thing.
Thirdly, and most seriously, your inner while examines the value of yes before it's been initialized. Either use a do while() construct, or intialize the value to something before the loop.
Fourthly, it's not clear what you are trying do to here. Do you really need two loops at all?

Answer 4

I think do while loop is all you need for the execution...
int main()
{
char yes,yn;
do
{
cout << "Hello world!" << endl;
cout<<"enter (Y/N): ";
cin>>yes;
yn = yes;
if(yn=='N'||yn=='n')
{
break;
}
}while(true);
}
your loop does not exit becuse your while loop is always true..
while(yn != 'y' || yn != 'Y' || yn != 'n' || yn != 'N')
Now I have added a break statement in your loop on a if condition and changed the do while condition
in this case it will run the loop on any condition and will exit the loop only when the user enter n or N

Answer 5

You did not initialize variable yn. So this statement
while(yn != 'y' || yn != 'Y' || yn != 'n' || yn != 'N')
has no sense and in fact it is unnecessary.
Try the following code
#include <iostream>
int main()
{
char yes_no;
do
{
std::cout << "\nHello world!" << std::endl;
std::cout<< "Do you want to repeat? (enter Y/N): ";
std::cin >> yes_no;
} while ( yes_no == 'y' || yes_no == 'Y' );
}

Answer 6

Thank you all for help. I have got what i wanted from all of you. Here is the final code running successfully. I have improved my code using suggestion from everyone of yours opinion.
int main()
{
char yes,yn;
do
{
.......... (main content of program, do things here.)
do
{
cout<<"Do again? (Y/N):";
cin>>yes;
yn = toupper(yes);
if(yn!='N' && yn != 'Y')
{
cout<<"Invalid selection"<<endl;
}
if(yn=='N' || yn == 'Y')
{
break;
}
}
while(true);
}
while(yn == 'Y');
}