passing variables of letters and numbers?

Projects Programming
2

You are missing arguments in your function definition. Try this...

void emon_status(char *device, byte status)
{
  if (client.connect(webserver,80))
  {
    client.print("GET /emoncms/input/post.json?apikey=xxxxxxxxxxxxxxxxxxxxxxxxxxx&json={");
    client.print(device);
    client.print(";");
    client.print(status);
    client.println("} HTTP/1.1");
    client.println("Host: avenant.net");
    client.println("User-Agent: Arduino-ethernet");
    client.println("Connection: close");
    client.println();
    client.stop();
  }
}