#include <iostream>
using namespace std;
int main()
{
    int a, b, c;
    cout << "please enter a,b,c" << endl;
    cin >> a >> b >> c;
    cout << "the biggest is ";
    int mid;
    {if (a > b)
        mid = a;
      {
        if (mid > c)

            cout << mid;
        else
            cout << c;
      }
      if (b > a)
          mid = b;
      {
          if (mid > c)
              cout << mid;
          else cout << c;
      }
    }
    system("pause");
    return 0;
}

明白了，没问题了。（但是，如果输入3 4 5后，它会输出两个5，这是怎么回事）