int myfun(int(*funpt)(int, int)){
    int sum = 0;
    for(int i = 0; i < 3; i++){
        sum += (*funpt)(i, i);
    }
    return sum;
}

int add(int a, int b){
    return a + b;
}

int num = myfun(add);

// how to pass paramter from outside to add
// int a=1, b=2;  add(a, b)

  
funpt is function pointer, (*funpt) is a function which have two parameters: int, int and return type is int. myfun only accept function pointer has the same signature, otherwise there is compiling error.

In order to assign a function to other function pointer. *funpt and add both have to have the same signature.

int(*funpt)(int, int);

int addMe(int a, int b){
    return a + b;
}

funpt = &addMe;
printf("num=%d\n", (*funpt)(1, 2));
printf("funpt=x%x\n", funpt);
printf("&add=x%x\n", &addMe);

  template<typename T1, typename T2>
    class MyTuple{
    public:
      T1 x;
      T2 y;
    public:
    MyTuple<T1, T2>(){
    }
    MyTuple<T1, T2>(T1 t1, T2 t2){
      x = t1;
      y = t2;
    }
  };

  unique_ptr<MyTuple<int, int>> tuplept(new MyTuple<int, int>(1, 2));
  cout<<"x="<<tuplept -> x<<endl;
  cout<<"y="<<tuplept -> y<<endl;