HackerRank C++ Class Templates problem solution

In this HackerRank C++ class templates problem in c++ programming You are given a main() function which takes a set of inputs. The type of input governs the kind of operation to be performed, i.e. concatenation for strings and addition for int or float. You need to write the class template AddElements which has a function add() for giving the sum of int or float elements. You also need to write a template specialization for the type string with a function concatenate() to concatenate the second string to the first string.

HackerRank C++ class Templates problem solution.

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <cassert>
using namespace std;

#include <utility>
#include <type_traits>

template <typename Type>
static constexpr bool allowed_types // variable tremplate
= std::is_same<Type, double>::value || std::is_same<Type, int>::value;

template <typename Type> class AddElements final {
    static_assert(allowed_types<Type>,
        "This type is not allowed. Only (double and int are allowed)");
    Type _var1;

public:
    explicit constexpr AddElements(const Type var1) noexcept 
           : _var1{ var1 } {}

    constexpr Type add(const Type var2) const noexcept
           { return _var1 + var2; }
};

template <> class AddElements<std::string> final {
    std::string _var1;

public:
    explicit AddElements(const std::string& var1) noexcept
                 : _var1{ std::move(var1) } {}

    std::string concatenate(const std::string& var2) const noexcept
    {
        return _var1 + var2;
    }
};

int main () {
  int n,i;
  cin >> n;
  for(i=0;i<n;i++) {
    string type;
    cin >> type;
    if(type=="float") {
        double element1,element2;
        cin >> element1 >> element2;
        AddElements<double> myfloat (element1);
        cout << myfloat.add(element2) << endl;
    }
    else if(type == "int") {
        int element1, element2;
        cin >> element1 >> element2;
        AddElements<int> myint (element1);
        cout << myint.add(element2) << endl;
    }
    else if(type == "string") {
        string element1, element2;
        cin >> element1 >> element2;
        AddElements<string> mystring (element1);
        cout << mystring.concatenate(element2) << endl;
    }
  }
  return 0;
}

Second solution

// template specialization
#include <iostream>
#include <string>
using namespace std;

// class template:
template <class T>
class AddElements {
    T element;
  public:
    AddElements (T arg) {element=arg;}
    T add (T x) {return x+element;}
};

// class template specialization:
template <>
class AddElements <string> {
    string element;
  public:
    AddElements (string arg) {element=arg;}
    string concatenate (string arg)
    {
      string s = element+arg;
      return s;
    }
};

int main () {
  int n,i;
  cin >> n;
  for(i=0;i<n;i++) {
    string type;
    cin >> type;
    if(type=="float") {
        double element1,element2;
        cin >> element1 >> element2;
        AddElements<double> myfloat (element1);
        cout << myfloat.add(element2) << endl;
    }
    else if(type == "int") {
        int element1, element2;
        cin >> element1 >> element2;
        AddElements<int> myint (element1);
        cout << myint.add(element2) << endl;
    }
    else if(type == "string") {
        string element1, element2;
        cin >> element1 >> element2;
        AddElements<string> mystring (element1);
        cout << mystring.concatenate(element2) << endl;
    }
  }
  return 0;
}