Function is_binary

example/general/stack_machine.cpp:37–41

   return number;
}
bool is_binary( const std::string &s )
{  char ch = s[0];
   bool binary = (strchr("+-*/.", ch) != 0);
   return binary;
}
bool is_variable( const std::string &s )
{  char ch = s[0];
   bool variable = ('a' <= ch) && (ch <= 'z');