Question

I’ve used python for a long time, and I’m just beginning to use C++

In python, if one has a set or a dictionary it is relatively easy to get a boolean value indicating whether or not a particular item is in that sequence using the in keyword.
i.e.

a = set(2,4,3)   
if 4 in a  
print "yes, 4 is in a, thank you for asking!"

it’s much more efficient than doing this:

a = [2,3,4]  
for number in a
>if number == 4  
>>return "yes, 4 is in a, thank you for asking!"

is there a way to do make a membership test simple and efficient in cpp or do you always have to iterate through some ordered sequence?

Answer 1

You have functionality like this in std::set and tr1::unordered_set (not yet in C++ standard).

#include <set>
#include <cstdio>

int main() {
     std::set<int> s;
     s.insert(1);        
     s.insert(2);
     s.insert(4);
     if (s.find(4) != s.end())
          puts("4 found!");
     return 0;
}

In reality, if your data set is small, linear search may still be the faster option.