关于C＋＋中Size和Capacity的问题

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

using namespace std;

int main(int argc, char *argv[]){    vector<int> c;    cout<<"INITIAL"<<endl;    cout<<"Size="<<c.size()<<endl;    cout<<"Capacity"<<c.capacity()<<endl;        cout<<"AFTER"<<endl;    for(int i=0;i<21;i++)    {      c.push_back(i);      cout<<"Size="<<c.size()<<endl;      cout<<"Capacity="<<c.capacity()<<endl;    }        system("PAUSE");    return EXIT_SUCCESS;}