c++ check all array values at once

Question

what I want to do is check an array of bools to see if 3 or more of them have been set to true. The only way I can think to do this is using a if statement for each possible combination of which there is lots because there are ten bools. Dose anybody have any suggestions on how best to do this.

Solution 1

The much easier way would be to loop through the array:

int numberOfSet = 0;
for( int i = 0; i < sizeOfArray; i++ ) {
     if( array[i] ) {
        numberOfSet++;
        //early cut-off so that you don't loop further without need
        // whether you need it depends on how typical it is to have
        // long arrays that have three or more elements set in the beginning
        if( numberOfSet >= 3 ) {
            break;
        }
     }
}

bool result = numberOfSet >= 3;

Solution 2

This would be the easiest way:

std::count(bool_array, std::end(bool_array), true) >= 3

Only problem is it keeps counting even after it has found 3. If that is a problem, then I would use sharptooth's method.

side note

I've decided to fashion an algorithm in the style of std::all_of/any_of/none_of for my personal library, perhaps you will find it useful:

template<typename InIt, typename P>
bool n_or_more_of(InIt first, InIt last, P p, unsigned n)
{
    while (n && first != last)
    {
        if (p(*first)) --n;
        ++first;
    }
    return n == 0;
}

For your purpose, you would use it like this:

n_or_more_of(bool_array, std::end(bool_array), [](bool b) { return b; }, 3);

Solution 3

Whenever you are setting an array element into TRUE value, you can increment a global counter. This will be the simplest way. At any point in your code, the global array will tell you the number of TRUE elements in the Array.

Another thing - if you are keeping upto 32 bool values, you can use a single int variable. int is 32 bits (in Win32) and you can store 32 bool.

char x = 0; //  00000000 // char is 8 bits

// TO SET TRUE
x = x | (1 << 4); // 00010000
x = x | (1 << 7); // 10010000

// TO SET FALSE
x = x & ~(1 << 4); // 10010000 & 11101111 => 10000000

// TO CHECK True/False
if( x & ~(1 << 4) )

Comments

[bobthemac]

does this mean that I need to use using namespace std and if so can I still use my current using namespace tle.

[Benjamin Lindley]

@bobthemac: If you're going to use something from the standard library, then you either prefix it with std:: as I did above. Or you have a using declaration in your file.

[Benjamin Lindley]

char? or CHAR? Either way, it's 8 bits. msdn.microsoft.com/en-us/library/aa505945.aspx

[Vishnu Haridas]

Yes, that's 8 bits, I was in a Java line, where char is 16 bits, to hold Unicode characters. Thanks for pointing out :-)