Correct way of defining/declaring templates in header file?

AFAIK, I am supposed to declare a class(and it's functions) in a header file, and then define them in it's respective .cpp file.

Here is my code.

C1.h

#ifndef C1_H_
#define C1_H_

namespace newspace {

class C1 {
public:
    void print();             //just a Hello World.
    template <typename T1>
    T1 power(T1 x, T1 y);     // calculate x^y
};

}

#endif 

C1.cpp

#include "C1.h"
#include<iostream>
namespace newspace {
void C1::print()                           // print() defined
{
    std::cout<<"Hello World"<<std::endl;
}
template <typename T1>
T1 C1::power(T1 x, T1 y)  //calculate x^y      // power() defined
{
    T1 ans=1;
    for (T1 i=0;i<y;i++)  
    {
        ans*=x;
    }
    return ans;
}
}

main.cpp

#include <iostream>
#include "C1.h"
using namespace std;
int main()
{
    newspace::C1 obj1;                 // created object obj1
    obj1.print();                      // works perfectly
    cout<<"Enter two numbers";
    int x,y;
    cin>>x>>y;
    cout<<obj1.power(x,y);             // gives error
    return 0;
}

The print() function works properly, but the templated function power() does not work and gives the error

undefined reference to `int newspace::C1::power<int>(int, int)'

What am I doing wrong here? what am I supposed to do?