If all you want to know is that is it a number or not do this. No LINQ is required
LINQ Way to check the numbers are between 0 and 9
if(yourstring.ToCharArray().Where(c=> c < '0' || c > '9').Any())
return false;
else
return true;
To check that it contains a valid number
double num;
if (double.TryParse(btn.Text, out num))
{
// It's a number!
}
or to check less than 10 without linq
static bool IsLessThanTen(string str)
{
foreach (char c in str)
{
if (c < '0' || c > '9')
return false;
}
return true;
}