Any built-in function to test if 4 is in [1,2,3,4] (vector)

Question

In Ruby I can do:

 [1,2,3,4].include?(4) #=>True

In Haskell I can do :

4 `elem`   [1,2,3,4]   #=> True

What should I do in C++?

Answer 1

Here an example using find:

#include <iostream>
#include <vector>
#include <algorithm>

int main() {
        std::vector<int> Num(4);
        //insert values
        Num[0]=1;
        Num[1]=2;
        Num[2]=3;
        Num[3]=4;
        std::vector<int>::iterator p = find(Num.begin(), Num.end(), 4);
        if (p == Num.end())
           std::cout  << "Could not find 4 in the vector"  << std::endl;
        else
           std::cout  << "Have found 4 in the vector"  << std::endl;
        return 0;
}

Answer 2

To get similar syntax as in OP's question:

std::vector<int> x;

if ( count( x.begin(), x.end(), VAL_TO_FIND ) ) {
 // found
} else {
 // not found 
}

Answer 3

You could use std::set This has a find() method.

Answer 4

There isn't a built-in function doing exactly that. There is std::find which comes close, but since it doesn't return a bool it is a bit more awkward to use.

You could always roll your own, to get syntax similar to JIa3ep's suggestion, but without using count (which always traverses the entire sequence):

template <typename iter_t>
bool contains(iter_t first, iter_t last, typename iter_t::value_type val){
    return find(first, last, val) != last;
}

Then you can simply do this to use it:

std::vector<int> x;

if (contains(x.begin(), x.end(), 4)) {...}

Answer 5

If the vector is ordered, you can also use std::binary_search.

std::binary_search(vec.begin(), vec.end(), 4)  // Returns true or false