Getch in combination with while-loop triggers loopcontent twice - c++

Question

I'm not really a programmer so my knownledge is extremely limited, I'm just hoping to get a very basic program working for a project. I've been googling around a lot and from what I've found I'm guessing it has to do with getch reading blank spaces or new lines as an input or something along those lines. None of the solutions I have found seem to fix the issue for me however (I might be implementing them wrong though).
This is in the main function:
while (roundNum <= 20)
{
roundNum++;
cout << roundNum / 2 << endl;
arrowKey();
}
And the arrowKey function (which I found by googling so I don) looks like this:
int arrowKey()
{
int c = 0;
switch ((c = _getch()))
{
case KEY_UP:
cout << endl << "Up" << endl;
break;
case KEY_LEFT:
cout << endl << "Left" << endl;
break;
case KEY_RIGHT:
cout << endl << "Right" << endl;
break;
case KEY_DOWN:
cout << endl << "Down" << endl;
break;
}
return 0;
}
The problem is that the roundNum reads out twice as well as adds two to the number for every arrow key press, like this:
1
1
Up
2
2
Right
3
3
etc
Help is greatly appreciated!

Answer 1

The problem is that a char can only hold 255 values. Thus, in order to get more unique values getch sometimes uses two values to represent a key code, an instruction and a value. For example, try hitting the F keys and you'll notice the same issue arise.
Ultimately, the behavior you are experiencing is due to the fact that getch is being called twice for the arrow keys.
To fix this, check if the instruction is for the arrow keys, in this case the value is 224 for the arrows keys. Once you have identified an arrow keys is being pressed read in the second value with another call to getch and there you will be able to find the actual key.
#include <iostream>
#include <conio.h>
using namespace std;
enum KeyCodes {
KEY_UP = 72,
KEY_LEFT = 75,
KEY_RIGHT = 77,
KEY_DOWN = 80
};
int arrowKey()
{
int c = _getch();
if (c == 224) {
//another value
int key = _getch();
switch (key)
{
case KEY_UP:
cout << endl << "Up" << endl;
break;
case KEY_LEFT:
cout << endl << "Left" << endl;
break;
case KEY_RIGHT:
cout << endl << "Right" << endl;
break;
case KEY_DOWN:
cout << endl << "Down" << endl;
break;
}
}
return 0;
}
int main() {
int roundNum = 0;
while (roundNum <= 20)
{
roundNum++;
cout << roundNum / 2 << endl;
arrowKey();
}
}
It's also worth pointing out that getch is not apart of the std library and could thus have some variation.