Bogo Sort - C++

#include <iostream>
#include <string>
#include <vector>
#include <cstdlib>

using namespace std;

bool is_sorted(const vector<char>& vec) {

    for (int i = 1, n = vec.size(); i < n; i++) {
        if (vec[i-1] > vec[i]) return false;
        // returns false if an element is smaller than one to its left
    }

    return true;
}

void shuffle(vector<char>& vec) {
    int i,n, tmp, rand_idx;

    for(i = 0, n = vec.size(); i < n; i++) {

        tmp = vec[i]; // store temporarily

        rand_idx = rand() % n; // pick a random index in the vector/array

        // swap each element in vector/array with another one that is chosen randomly
        vec[i] = vec[rand_idx];
        vec[rand_idx] = tmp;
    }
}

void bogosort(vector<char>& vec) {
    while( !is_sorted(vec) ) shuffle(vec);
}

int main() {
    cout << "give me a string" << endl;
    string s; getline(cin, s);

    vector<char> vec(s.begin(), s.end());

    if (!vec.empty()) bogosort(vec);

    string str(vec.begin(), vec.end());

    cout << str << endl;
    return 0;
}