Adding Double, String value on listbox.

Question

Hello,

I'm trying to make listbox show a few string and double values when button is pressed.

However, I'm  getting errors: Cannot implicitly convert type 'string' to 'double' When ever I put double agestr = ageText.Text;

How can I make it so agestr and teethstr text box only accepts double values? 

 

private void addButton_Click(object sender, EventArgs e)

{ 

string namestr = nameText.Text;

string agestr = ageText.Text;    //This needs to be double, not  string

string genderstr = genderList.Text;

string teethstr = teethText.Text;  //This needs to be double, not string

string tailstr = tailText.Text; 

 

string row = String.Format("{0} {1} {2} Has {3} teeth. tail is {4} cm long", namestr, agestr, genderstr, teethstr, tailstr);

listBox.Items.Add(row);

}