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A little help?
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; } }
16 Answers
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~ 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
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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.
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~ 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.
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~ swim ~ it doesn't wait, it fail to extract the input and set a to 0
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~ 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.
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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
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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 đ
but the problem remains...
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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
}
0
~ swim ~ what happens if I press enter?
DIMITRIS_PLAYS you should edit your question and correct to
while (!quit) {...
As you really intended.
0
And a? What value has been assigned? Does it wait till an integer is provided or does it continue through the program?