Scrolling menu in the console - c++

Question

There is the menu in the console navigating by arrows UP-DOWN. Problem: when I select "Enter number" and the result disappears, I can't select another menu item. How to fix it?
Here is my C++ code:
#include <iostream>
#include <string>
#include <windows.h>
using namespace std;
int main()
{
string Menu[2] = {"Enter number", "Exit"};
int pointer = 0;
while(true)
{
system("cls");
SetConsoleTextAttribute(GetStdHandle(STD_OUTPUT_HANDLE), 15);
cout << "Main Menu\n\n";
for (int i = 0; i < 2; ++i)
{
if (i == pointer)
{
SetConsoleTextAttribute(GetStdHandle(STD_OUTPUT_HANDLE), 11);
cout << Menu[i] << endl;
}
else
{
SetConsoleTextAttribute(GetStdHandle(STD_OUTPUT_HANDLE), 15);
cout << Menu[i] << endl;
}
}
while(true)
{
if (GetAsyncKeyState(VK_UP) != 0)
{
pointer -= 1;
if (pointer == -1)
{
pointer = 1;
}
break;
}
else if (GetAsyncKeyState(VK_DOWN) != 0)
{
pointer += 1;
if (pointer == 2)
{
pointer = 0;
}
break;
}
else if (GetAsyncKeyState(VK_RETURN) != 0)
{
switch (pointer)
{
case 0:
{
int number;
cout << "\nEnter number --> ";
cin >> number;
cout << "\nThe number is ";
cout << number;
Sleep(1000);
} break;
case 1:
{
return 0;
} break;
}
break;
}
}
Sleep(150);
}
return 0;
}
Maybe, it will be better to use Qt::Key instead of GetAsyncKeyState?

Answer 1

The problem is GetAsyncKeyState,
MSDN tells us:
If the function succeeds, the return value specifies whether the key
was pressed since the last call to GetAsyncKeyState, and whether the
key is currently up or down. If the most significant bit is set, the
key is down, and if the least significant bit is set, the key was
pressed after the previous call to GetAsyncKeyState.
So in your case, you pressed Enter to get your number, so the enter key has been pressed since the last call, so (GetAsyncKeyState(VK_RETURN) != 0) is always true.
You should have look more precisely on the return of GetAsyncKeyState to see if the key is really pressed, or to do nothing if the key was already pressed in the call just before. Be careful with the last option, other apps or threads can also call GetAsyncKeyState.

Answer 2

The reason why your result disappears when you select "Enter Number" is because you reinitialize the output buffer with the new string every time you press the "Up Arrow". You can get around this by turning this into a FSM logic where you are in control of the states and your next state is dependent on the current and previous state. At the moment, your logic only cares about the current state.

Answer 3

To be sure to test if a key is pressed at a moment, use:
short result;
result = GetAsyncKeyState(VK_RETURN);
if (result & 0x8000) { ... }
or
if (GetAsyncKeyState(VK_RETURN) & 0x8000) { ... }
I tried this at home but it seems Javia1492 is right, you also have a buffer problem I didn't know. Try not to use "system("cls")", it's old C. try to write your own clearing function like the following found on MSDN:
void cls( HANDLE hConsole )
{
COORD coordScreen = { 0, 0 }; // home for the cursor
DWORD cCharsWritten;
CONSOLE_SCREEN_BUFFER_INFO csbi;
DWORD dwConSize;
// Get the number of character cells in the current buffer.
if( !GetConsoleScreenBufferInfo( hConsole, &csbi ))
{
return;
}
dwConSize = csbi.dwSize.X * csbi.dwSize.Y;
// Fill the entire screen with blanks.
if( !FillConsoleOutputCharacter( hConsole, // Handle to console screen buffer
(TCHAR) ' ', // Character to write to the buffer
dwConSize, // Number of cells to write
coordScreen, // Coordinates of first cell
&cCharsWritten ))// Receive number of characters written
{
return;
}
// Get the current text attribute.
if( !GetConsoleScreenBufferInfo( hConsole, &csbi ))
{
return;
}
// Set the buffer's attributes accordingly.
if( !FillConsoleOutputAttribute( hConsole, // Handle to console screen buffer
csbi.wAttributes, // Character attributes to use
dwConSize, // Number of cells to set attribute
coordScreen, // Coordinates of first cell
&cCharsWritten )) // Receive number of characters written
{
return;
}
// Put the cursor at its home coordinates.
SetConsoleCursorPosition( hConsole, coordScreen );
}