c# textBox1.Text converting to KeyCode and send it to a chat program with SendMessage

Question

I have a Textbox1 and I want send its text to a program that is working by Virtual Keys.

I have these :

const uint MAPVK_VK_TO_CHAR = 0x02;
public const int WM_SETTEXT = 0x100;

[DllImport("user32.dll", CharSet = CharSet.Auto)]
public static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, IntPtr lParam);

[DllImport("user32.dll", CharSet = CharSet.Auto)]
public static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, int wParam, stringBulder lParam);
[DllImport("user32.dll", CharSet = CharSet.Auto)]
public static extern int MapVirtualKey(int uCode, uint uMapType); 

int txL = textBox1.TextLength;
for (int o = 0; o < (txL-0); o++)
{
     int key = MapVirtualKey((int)textBox1.Text[o], MAPVK_VK_TO_CHAR);
     SendMessage(hwndTarget, WM_SETTEXT, key, new StringBuilder(key.ToString());
}

I just want to know if any function exists that can convert any char of TextBox to KeyCode ? I could write a switch : case but this will be too long. (it contain all unicodes languages too :S)