Section: String Functions
isdigit functions returns a logical array that is 1 
for characters in the argument string that are digits, and 
is a logical 0 for characters in the argument that are not
digits.  The syntax for its use is
x = isdigit(s)
where s is a string.  
isdigit:
--> isdigit('numb3r5')
ans = 
 0 0 0 0 1 0 1