I've been able to find a solution
UPDATE:
Answer posted by OP:
private void button1_Click(object sender, EventArgs e)
{
String user = this.textBox1.Text;
String pass = this.textBox2.Text;
String status = this.comboBox1.SelectedItem.ToString();
WMSDService cf = new WMSDService();
String hasil = cf.checkStatusUser(user, pass, status);
if (hasil== "C")
{
Consumer st = new Consumer();
st.Show();
this.Hide();
}
else if (hasil == "yes")
{
Forestry st = new Forestry();
st.Show();
this.Hide();
}
else if (hasil == "CO")
{
Corporation st = new Corporation();
st.Show();
this.Hide();
}
else if (hasil == "CU")
{
Customs st = new Customs();
st.Show();
this.Hide();
}
else {
MessageBox.Show("Login Failed");
}}