using keybd_event to send virtual key code

send_key.cs

using System;
using System.Runtime.InteropServices;

[DllImport("user32.dll")]
static extern void keybd_event(byte bVk, byte bScan, uint dwFlags, uint dwExtraInfo);

void PressKey(byte keyCode)
{
    const int KEYEVENTF_EXTENDEDKEY = 0x1;
    const int KEYEVENTF_KEYUP = 0x2;
    keybd_event(keyCode, 0x45, KEYEVENTF_EXTENDEDKEY, 0);
    keybd_event(keyCode, 0x45, KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP, 0);
}

// to send backspace key use: PressKey((byte) '\b');