#include<iostream.h>
template <class numtype>
class Compare
{
    public:
        Compare(numtype a,numtype b)               //  这里是干吗用的？
        {
            x=a;
            y=b;
        }                                            // 到这里
        numtype max()
        {
            return (x>y)?  x:y;
        }
        numtype min()
        {
            return (x<y)?  x:y;
        }
    private:
        numtype x,y;
};
int main()
{
    Compare <int> cmpl(3,7);
    cout<<cmpl.max()<<"max"<<endl;
    cout<<cmpl.min()<<"min"<<endl;
    Compare <float> cmp2(45.78,93.6);
    cout<<cmp2.max()<<"max"<<endl;
    cout<<cmp2.min()<<"min"<<endl;
    Compare <char> cmp3('a','B');
    cout<<cmp3.max()<<"max"<<endl;
    cout<<cmp3.min()<<"min"<<endl;
    return 0;
}

这是在定义构造函数，在形参列表中用虚拟类型numtype代替了实际类型，当你在main中使用Compare <int> cmpl(3,7);
时，用实际类型Int代替了numtype！

谢谢。太不小心了。
前面有一段这样的

class Compare_int
{
    public:
        Compare(numtype a,numtype b)               //  这里是干吗用的？
        {
            x=a;
            y=b;
        }                                            // 到这里
        numtype max()
        {
            return (x>y)?  x:y;
        }
        numtype min()
        {
            return (x<y)?  x:y;
        }
    private:
        numtype x,y;
};


那里很奇怪，可例题又变回构造函数了。没看清楚，问了个这么傻得问题，汗.