c++ vector实例

#include <iostream>
#include <string>
#include <vector>
#include <iostream>
using std::cout;
using std::cin;
using std::endl;
using std::vector;
using namespace std;

int main()
{
    string s = "hell";
    string w = "worl!";
    s = s + w; //s +=w;
    for (int ii = ; ii != s.size(); ii++)
    {
        cout << ii << " " << s[ii];
    }
    cout << endl;

    string::const_iterator cii;
    int ii = ;
        for (cii = s.begin(); cii != s.end(); cii++)
    {
        cout << ii++ << " " << *cii << endl;
    }

    vector<double> student_marks;

    int num_students;
    cout << "Number of students: " << endl;
    cin >> num_students;    

    student_marks.resize(num_students);

    for (vector<double>::size_type i = ; i < num_students; i++)
    {
        cout << "Enter marks for student #" << i +
            << ": " << endl;
        cin >> student_marks[i];
    }

    cout << endl;
    for (vector<double>::iterator it = student_marks.begin();
        it != student_marks.end(); it++)
    {
        cout << *it << endl;
    }

    return ;
}  

0 h1 e2 l3 l4 w5 o6 r7 l8 !
0 h
1 e
2 l
3 l
4 w
5 o
6 r
7 l
8 !
Number of students:

3
Enter marks for student #1:
3
Enter marks for student #2:
2
Enter marks for student #3:
6

3
2
6