C++基本序列式容器

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

int main()
{
    vector< int > num;
    num.push_back( 50 );
    num.insert(num.begin(), 10);
    num.insert(num.end(), 20);
    num.push_back( 60 );
    num.push_back( 40 );
    cout << num.size() << endl;
    for(int i = 0; i < num.size(); i++)
        cout << num[i] << " ";
    cout << endl;
    num.erase(num.begin());
    cout << num.size() << endl;
    for(int i = 0; i < num.size(); i++)
        cout<< num[i] <<" ";
    cout << endl;
    return 0;
}

5
10 50 20 60 40 
4
50 20 60 40