How to simulate a key press in C++

It looks like you want to use either SendInput() or keybd_event() (which is an older way of doing the same thing).

First - find this answer on how to use sendinput function in C++.

Look at the code section:

// ...    INPUT ip;// ...    // Set up a generic keyboard event.    ip.type = INPUT_KEYBOARD;    ip.ki.wScan = 0; // hardware scan code for key    ip.ki.time = 0;    ip.ki.dwExtraInfo = 0;    // Press the "A" key    ip.ki.wVk = 0x41; // virtual-key code for the "a" key    ip.ki.dwFlags = 0; // 0 for key press    SendInput(1, &ip, sizeof(INPUT));// ...

I didn't understand where the magic number 0x41 came from.

Go to SendInput documentation page. Still don't understand where's the 0x41.

Go to INPUT documentation and from there to KEYBDINPUT documentation. Still no magic 0x41.

Finally go to Virtual-Key Codes page and understand that Microsoft has given the names for Ctrl (VK_CONTROL), Alt (VK_MENU), F1-F24 (VK_F1 - VK_F24, where are 13-24 is a mystery), but forgot to name characters. Actual characters have codes (0x41-0x5A), but don't have names like VK_A - VK_Z I was looking for in winuser.h header.

It is a virtual-key code for the key "A" as the comment says. It is just what Windows' developers decided the numeration shall be. Here is a link with all the keys where 0x41 is documented as A.