栈的使用，rails

1.栈的使用

2.一种做题方式，在草纸上人工做，想清楚先后顺序，然后让机器做

#include <stdio.h>
#include <iostream>
#include <stack>

using namespace std;
int num[1000];

int main()
{
    int a, i, j;
    while(scanf("%d", &a) != EOF)
    {
        if ( a == 0 )
            break;
        while(scanf("%d", &num[0]))
        {
            if(num[0] == 0)
            {
                cout << endl;
                break;
            }

            for(i = 1; i < a; i ++)
                cin >> num[i];

            stack <int> st;
            int now = 0;
            int ok = 1;
            for ( i = 0; i < a; i++ )
            {
                if ( now < num[i] )
                {
                    for ( j = now + 1; j <= num[i]; j++ )
                        st.push(j);
                    st.pop();
                    now = num[i];
                }
                else
                {
                    if(st.top() != num[i])
                    {
                        ok = 0;
                        break;
                    }
                    else st.pop();
                }
            }

            if ( ok == 0) cout << "No" << endl;
            else cout << "Yes" << endl;
        }

    }
    return 0;
}