Try this..
int countAnswers = 0;
List<TextBox> lstText =new List<TextBox> ();
var controls = this.Controls.OfType<TextBox>().ToArray();
for (int i = 0; i < controls.Length; i++)
{
if (controls[i].Name == "textBox" + i)
lstText.Add(controls[i]);
}
string[] answers = { "a", "b", "c", "d", "e", "f", "g", "h", "i", "j" };
for (int i = 0; i < 10; i++)
{
if (lstText[i].Text == answers[i])
countAnswers ++;
}
int countWrong = lstText.Count - countAnswers;