Why can't I read all Ctrl + 'letters' - c++

Question

I've made a program that allows me to read all the stand-alone function keys (that I thought to test, at least) on my keyboard. I have it designed so that I can refer to any single key input as a single value. It handles Return, F1-F12, delete, backspace, arrows etc
I just thought to test modifications of input. I already made sure shift works, but now I decided to test Ctrl and Alt.
Question 1
Why does Alt not modify any of the input key codes?
Question 2
Why can I not capture certain Ctrl + combinations?
Eg. Ctrl + s; Ctrl + 1-9;
Ctrl + 2 works, but I think it might be due to having my keyboard set as UK.
This is the code I am using.
Please note, I am not necessarily asking how to capture these key combinations (unless it is a simple modification or two). I only want to know why I am unable to.
#include <iostream>
#include <conio.h>
#include <cwchar>
union wide_char
{
short Result;
char C[2];
};
int main()
{
wchar_t R;
int N;
wide_char user_input;
//Loops forever, this is only a proof of concept program proving this is possible to incorporate into a larger program
while(true)
{
user_input.C[0] = 0;
user_input.C[1] = 0;
//Loop twice, or until code causes the loop to exit
//Two times are neccessary for function keys unfortunately
for(int i = 0; i < 2; ++i)
{
//While there isn't a key pressed, loop doing nothing
while(!kbhit()){}
//Grab the next key from the buffer
//Since the loop is done, there must be at least one
user_input.C[i] = getch();
switch(user_input.C[i])
{
case 0:
case -32:
//The key pressed is a Function key because it matches one of these two cases
//This means getch() must be called twice
//Break switch, run the for loop again ++i
break;
default:
//The character obtained from getch() is from a regular key
//Or this is the second char from getch() because the for loop is on run #2
//Either way we need a wide char (16 bits / 2 Bytes)
if(user_input.C[1] != 0)
//Function keys {Arrows, F1-12, Esc}
//We now combine the bits of both chars obtained
//They must be combined Second+First else the F1-12 will be duplicate
//This is because on F1-12 getch() returns 0 thus won't affect the combination
R = user_input.Result;
else
//Regular key press
R = user_input.C[0];
//Display our unique results from each key press
N = R;
std::cout << R << " R = N " << N << std::endl;
if( R == 'a' )
std::cout << "a = " << N << std::endl;
//Manually break for loop
i = 3;
break;
}
}
//We need to reset the array in this situation
//Else regular key presses will be affected by the last function key press
}
}

Answer 1

This is very specific to your environment. You're using conio which is specific to DOS / Windows.
Most of the Ctrl + alpha key values are bound to characters 1 - 26, and certain others are bound to other values under 31, to map to ASCII control characters. But some, like Ctrl + S have special meaning (Ctrl + S is XOFF in ASCII), and so might get 'eaten' by your environment.
Fundamentally, the issue you're facing is the fact that getch approximates an old-school serial terminal interface. They only expose keyboard events at a "least common denominator" level, as opposed to a lower level that would allow you to distinguish modifier keys, etc. and give you a better way to deal with special keys such as function keys.
(As you've noticed, function keys, have special multi-byte sequences. Again, this is due to emulating old-school serial terminals, where the keyboard might be at the other end of a remote link.)
To get a lower-level (and therefore more direct and flexible interface) you need to use a more platform-specific library, or a richer library such as SDL. Either would give you a lower level view of the inputs from the keyboard.