template报错不明白？

c++萌新 template报错

#include<bits/stdc++.h>
using namespace std;
template<size_t SIZE>
class HP{
    private:
        size_t Len;
        bool ifPlus;
        short hp[SIZE];
    public:
        void clear(){
            int i;
            ifPlus = true;
            Len = 0;
            for(i=0; i<Len; ++i) hp[i] = 0;
        }
        HP operator=(HP<size_t aSize> a){
            int i;
            clear();
            ifPlus = a.ifPlus;
            Len = a.Len;
            if(SIZE < a.Len){
                printf("Out of memory!");
                exit(0);
            }
            for(i=0; i<a.Len; ++i) hp[i] = a.hp[i];
            return temp;
        }

信息：

[Error] template argument 1 is invalid

[Error] template argument 1 is invalid （他说了两遍)

[Error] 'HP' is not a template

[Error] expected primary-expression before 'aSize'

[Error] expected '>' before 'aSize'

谢谢大佬

#include <iostream>
using namespace std;

#include<bits/stdc++.h>
using namespace std;
template<size_t SIZE>
class HP{
    private:
        size_t Len;
        bool ifPlus;
        short hp[SIZE];
    public:
        void clear(){
            int i;
            ifPlus = true;
            Len = 0;
            for(i=0; i<Len; ++i) hp[i] = 0;
        }
        HP operator=(HP a){
            int i;
            clear();
            ifPlus = a.ifPlus;
            Len = a.Len;
            if(SIZE < a.Len){
                printf("Out of memory!");
                exit(0);
            }
            for(i=0; i<a.Len; ++i) hp[i] = a.hp[i];
            HP temp;
            return temp;
        }

};

int main() {
    // your code goes here
    return 0;
}