try this
var sepString=(textBox1.Text).Split('/');
var index=1;
String[] month = new String[] { "month", "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December" };
while (index > 13)
{
if (sepString[0] == index)
{
m = month[index].ToString();
break;
}
else
{
index++;
}
m;
}