Please help, I can’t figure out why my code isn’t working.
error: invalid use of incomplete type ‘class StatePair’
31 | StatePair<T1, T1>::StatePair(){
| ^
main.cpp:61:33: error: ‘endl’ was not declared in this scope
61 | cout << key << “: ” << value << endl;
| ^~~~

CODE:

#define STATEPAIR

using namespace std;

template<typename T1, typename T2>
class StatePair {

public:

   StatePair();

   StatePair(T1 userKey, T2 userValue);

   void SetKey(T1 newkey);
  
   void SetValue(T2 newVal);

   T1 GetKey();

   T2 GetValue();

   void PrintInfo();
   
public:
   T1 key;
   T2 value;
};

template<typename T1, typename T2>
StatePair<T1, T1>::StatePair(){
}

template<typename T1, typename T2>
StatePair<T1, T2>::StatePair(T1 userKey, T2 userValue) {
     key = userKey;
     value = userValue;
}

template<typename T1, typename T2>
void StatePair<T1, T2>::SetKey(T1 newKey) {
     key = newKey;
}

template<typename T1, typename T2>
void StatePair<T1, T2>::SetValue(T2 newVal){
     value = newVal;
}
template<typename T1, typename T2>
T1 StatePair<T1, T2>::GetKey() {
return key;
}

template<typename T1, typename T2>
T2 StatePair<t1, T2>::GetValue() {
return value;
}

//TODO: Define PrintInfo() method

template<typename T1, typename T2>
void StatePair<T1, T2>::PrintInfo() {
cout << key << ": " << value << endl;
}

````#endif

I've added namespace std thinking that would solve my issues.