Taking the elements that are > 0 from 1 array to another - c++

Question

I make the user to type maximum elements and then enter that elements into first array p,then I want to take only the elements that are bigger than 0 and transfer them to a new array w. Here's the code and where exactly I make mistake:
void main(){
int p[10], w[10], n,i,j;
cout << "Maximum elements: "; cin >> n;
for (i = 0; i < n; i++){
cout << "Enter " << i << "-nd element"; cin >> p[i];
}
j = 0;
for (i = 0; i < n; i++){
if (p[i] > 0){
w[j] = p[i];
j++;
}
for (j = 0; j < n; j++){
cout << w[j];
}
}
system("pause");
}

Answer 1

In:
for (i = 0; i < n; i++){
if (p[i] > 0){
w[j] = p[i];
j++;
}
for (j = 0; j < n; j++){
cout << w[j];
}
}
the inner loop is printing every element of the array w. That loop is executed for every element of p (being it inside the outer for loop).
This mean that, for example, the first time it visits p to check if the first element is 0, it may assign w[0] and then go on and print all the elements of w. Problem is that w is not initialised at that point, so what you see is random garbage (probably).
Just move the loop outside and make it so it only prints the part of the array that is populated:
for (i = 0; i < n; i++){
if (p[i] > 0){
w[j] = p[i];
j++;
}
}
for (int k = 0; k < j; k++){
cout << w[k];
}
Live demo
Also learn how to use std::vector or std::array and the algorithms in <algorithm>.
Also remember that main has return type int.

Answer 2

Using std::copy_if from <algorithm> do the job you want, as in the example provided in http://www.cplusplus.com/reference/algorithm/copy_if/:
// copy_if example
#include <iostream> // std::cout
#include <algorithm> // std::copy_if, std::distance
#include <vector> // std::vector
int main () {
std::vector<int> foo = {25,15,5,-5,-15};
std::vector<int> bar (foo.size());
// copy only positive numbers:
auto it = std::copy_if (foo.begin(), foo.end(), bar.begin(), [](int i){return !(i<0);} );
bar.resize(std::distance(bar.begin(),it)); // shrink container to new size
std::cout << "bar contains:";
for (int& x: bar) std::cout << ' ' << x;
std::cout << '\n';
return 0;
}
For you code, the problem is that you modify j in the printing loop whereas it is primary used as output index. Try to reduce scope of your local variable to out spot those issues, creating sub function may also help.
Finnaly, your fixed code may be something like:
void main(){
std::cout << "Maximum elements: ";
int n;
std::cin >> n;
int p[10];
for (int i = 0; i < n; i++){
std::cout << "Enter " << i << "-nd element";
std::cin >> p[i];
}
int w[10];
int w_size = 0;
for (int i = 0; i < n; i++){
if (p[i] > 0){
w[w_size] = p[i];
w_size++;
}
}
for (int i = 0; i < w_size; i++){
std::cout << w[i];
}
system("pause");
}