A little help?

Question

So I coded a feature which says to the user if he wants to exit the program by typing zero(0).It works perfect on the test subject but when I put the same line of code to a pre-existing app that I had previously made it doesn't work, in fact it skips completely the function of asking the user to put the number 0 and the program terminates by it self. The code:
bool quit=0;
while(!quit)
{
cout<<"Press the '0' key to terminate the programm"<<endl;
int a;
cin >> a;
if(a <=0)
{
return 0;
}

}

Answer 1

~ swim ~ as usual you are very competent!
I tried and the results are:
If I input a char or a string it assigns 0 and exit.

With enter or space or nothing it prints 8 infinite times.
I don't know if it is garbage or what at this point.
[EDIT if I initialize a to 7 for example and I enter nothing it prints 7 infinite times ]

With noskipws instead it assigns 0

So it seems like it sets failbit and assign 0 if I enter wrong inputs, it skips if I don't provide input, e.g. space,enter

I have also noticed that if I enter one valid input for example 2 it assigns 2 and print it infinitely

Anyway it doesn't wait.. it proceed and loops infinitely

P.s. I have added a cout<< at the end of while block

Answer 2

bool quit=0
while(!quit<1)

The ! means not. So this means: While quit is not lower than 1.

But it is lower than 1 to begin with, so the code is not executed.

Answer 3

~ swim ~ yes you are right !
It was undefined behaviour , but from C++11 it is set to 0 in case it fails to convert input.

Anyway I think leaving uninitialized variables is a bad habit, potentially leading to UB.

Answer 4

~ swim ~ it doesn't wait, it fail to extract the input and set a to 0

Answer 5

~ swim ~ yes , it should wait for input but it's not, at least here on code playground.
That's why I was a bit confused.

Maybe due to the system forward input , seems like cin gets fed up on every iteration of the while loop.

For the white space / enter I got the same result(discarded) but on my tests an 8 or previous value is assigned even if I clear and flush , I don't think it's garbage, probably something else.

Anyway there's no reason to struggle with all of this, since this kind of programs are managed in a different way and streams aren't intended for key events.

Answer 6

Try it like this, you can freely choose to use `break` to exit the loop, or `return` statement to exit a function. I used `break` here because I didn't see the code placed in a function.

int a;

while(true)
{
cout << "Press the '0' key to terminate the programm" << endl;
cin >> a;
if(a <= 0)
{
break;
}
}

Hth, cmiiw

Answer 7

The code was ment to start with:
bool quit=0;
while(!quit)
And not:
bool quit=0;
while(!quit<1)
Sorry for that I got distracted and typed wrong 😊
but the problem remains...

Answer 8

1 Undefined Behaviour : a is local uninitialized, some compiler may default to 0.

2 A key should be of char type, or enumerated.

3 declare a every iteration is not good from my point

for ( char a = 0 ; !quit ; ){
cin >> a;
If ( '0' == a ) return 0; // better quit = 1
}

Answer 9

~ swim ~ what happens if I press enter?
DIMITRIS_PLAYS you should edit your question and correct to
while (!quit) {...
As you really intended.

Answer 10

And a? What value has been assigned? Does it wait till an integer is provided or does it continue through the program?