Availability:built-in
string_code(?Index, 
+String, ?Code)True when Code represents the character at the 1-based Index 
position in String. If Index is unbound the string 
is scanned from index 1. Raises a domain error if Index is 
negative. Fails silently if Index is zero or greater than the 
length of
String. The mode string_code(-,+,+) is 
deterministic if the searched-for Code appears only once in String. 
See also
sub_string/5.