If-elseif-else Logic Question

Question

I have a set of three values, call them x, y, and z. If value A happens to match only one in the set x, y, and z, then that means we have a proper match and we stop searching for a match, even if it is at y. It can match any one in that set. These values x, y, and z are non-constant so I cannot use a switch-case statement.

How do I do this with an if-elseif-else statements without having to use GOTO. I am using C++ (no boost or any of that other fancy stuff).

Now, I am trying to do this in code and it is racking my brain this morning (not enough coffee?)

Answer 1

Um:

if ( a == x || a == y || a == z ) {
   // whatever
}

Or am I missing something?

Answer 2

In PHP, I'd do if(in_array('A', array($x, $y, $z)) { }. I imagine you can do something similar in C++.

Answer 3

The || operator in C++ short-circuits and will stop evaluating as soon as it hits true, so:

if (a==x || a==y || a==z)
{
}

Will do exactly what you want.

Answer 4

Most efficient way I can think of, assuming I understood your question rightly:

int mx = a == x, my = a == y, mz = a == z;
if (mx + my + mz == 1) {
    if (mx) {
        // x
    } else if (my) {
        // y
    } else {
        // z
    }
} else {
    // no match
}

Answer 5

STL has std::set. std::set has find().

Answer 6

By non-constant do you mean you may have [X], or you may have [X,Y] or you may have [X...]

If so put the values into a vector and use binary_search (both vector and binary_search are in STL)

Vector<int> itemVec;
itemVec.push_back(x);
//push values as needed

if( binary_search( itemVec.begin(), itemVec.end(), a)
{
   //do something
}