C#でSendInputを使う

SendKey.cs

using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;

class SendKey {

    [StructLayout(LayoutKind.Sequential)]
    private struct MOUSEINPUT {
        public int dx;
        public int dy;
        public int mouseData;
        public int dwFlags;
        public int time;
        public int dwExtraInfo;
    };

    [StructLayout(LayoutKind.Sequential)]
    private struct KEYBDINPUT {
        public short wVk;
        public short wScan;
        public int dwFlags;
        public int time;
        public int dwExtraInfo;
    };

    [StructLayout(LayoutKind.Sequential)]
    private struct HARDWAREINPUT {
        public int uMsg;
        public short wParamL;
        public short wParamH;
    };

    [StructLayout(LayoutKind.Explicit)]
    private struct INPUT {
        [FieldOffset(0)]
        public int type;
        [FieldOffset(4)]
        public MOUSEINPUT no;
        [FieldOffset(4)]
        public KEYBDINPUT ki;
        [FieldOffset(4)]
        public HARDWAREINPUT hi;
    };

    [DllImport("user32.dll")]
    private extern static void SendInput(int nInputs, ref INPUT pInputs, int cbsize);
    [DllImport("user32.dll", EntryPoint = "MapVirtualKeyA")]
    private extern static int MapVirtualKey(int wCode, int wMapType);

    private const int INPUT_KEYBOARD = 1;
    private const int KEYEVENTF_KEYDOWN = 0x0;
    private const int KEYEVENTF_KEYUP = 0x2;
    private const int KEYEVENTF_EXTENDEDKEY = 0x1;

    private void Send(Keys key, bool isEXTEND) {
        /*
         * Keyを送る
         * 入力
         *     isEXTEND : 拡張キーかどうか
         */

        INPUT inp = new INPUT();

        // 押す
        inp.type = INPUT_KEYBOARD;
        inp.ki.wVk = (short)key;
        inp.ki.wScan = (short)MapVirtualKey(inp.ki.wVk, 0);
        inp.ki.dwFlags = ((isEXTEND) ? (KEYEVENTF_EXTENDEDKEY) : 0x0) | KEYEVENTF_KEYDOWN;
        inp.ki.time = 0;
        inp.ki.dwExtraInfo = 0;
        SendInput(1, ref inp, Marshal.SizeOf(inp));

        System.Threading.Thread.Sleep(100);

        // 離す
        inp.ki.dwFlags = ((isEXTEND) ? (KEYEVENTF_EXTENDEDKEY) : 0x0) | KEYEVENTF_KEYUP;
        SendInput(1, ref inp, Marshal.SizeOf(inp));
    }

    static void Main() {
        System.Threading.Thread.Sleep(2000);
        SendKey s = new SendKey();
        s.Send(Keys.Z, false);
        s.Send(Keys.Left, true);
    }
}