binary search

#include <iostream>
#include <vector>
using namespace std;

int b_search(vector<int> a, int val) {
    int l = 0, r = a.size() - 1;
    while (r > l) {
        int mid = (l + r) / 2;
        if (a[mid] < val)
            l = mid + 1;
        else if (a[mid] > val)
            r = mid - 1;
        else
            return mid;
    }
    return l;
}

int main() {
    vector<int> a = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
    cout << b_search(a, 4);
    return 0;
}