Заменить положительные элементы вектора А(10) нулями

int j=0;
for (int i=0; i<10; i++;)
if(a[i]>=0){a[i]=o;j++;}
cout<<j;

#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <functional>
#include <cstdlib>
#include <ctime>
 
class Random {
    int hi;
    int lo;
public:
    Random(int h, int l) : hi(h), lo(l) {}
    int operator () () { return rand() % ( hi - lo + 1 ) + lo; }
};
 
int main(){
    std::vector<int> vec(10);
    srand(time(NULL));
    std::generate(vec.begin(), vec.end(), Random( 10, -10));
    std::cout << "Before:" << std::endl;
    std::copy(vec.begin(), vec.end(), std::ostream_iterator<int>(std::cout, " "));
    std::cout << std::endl;
    std::replace_if(vec.begin(), vec.end(), std::bind2nd(std::greater<int>(), 0), 0);
    std::cout << "After:" << std::endl;
    std::copy(vec.begin(), vec.end(), std::ostream_iterator<int>(std::cout, " "));
    std::cout << std::endl;
    std::cout << std::count(vec.begin(), vec.end(), 0) << " zero elements." << std::endl;
    return 0;
}

#include <iostream>
#include <vector>
#include <iterator>
#include <algorithm>
 
int main()
{
    srand(static_cast<unsigned>(time(0)));
    std::vector<int> vec(10);
    std::generate(vec.begin(), vec.end(), [] () {return rand() % (5 + 5 + 1) -5;});
    std::replace_if(vec.begin(), vec.end(), [] (const int val) {return val > 0;}, 0);
    std::cout << std::count(vec.begin(), vec.end(), 0) << std::endl;
}