C++ Function to find the min+max value element in a vector

Question

I just started learning C++ so I am very new to this.

I have a vector vector<int> pricelist{30,10,16,25,13}; that's stored in a main class.

I want to implement a function lowestNHighestPrices() to return a Prices object that gives me the index value of the highest and lowest values in the vector (ie 0 and 1 respectively).

class Prices {
  protected:
   int lowestPrice;
   int highestPrice;

  public:
   Prices(const int lowestPriceIn, const int highestPriceIn)
       : lowestPrice(lowestPriceIn), highestPrice(highestPriceIn) {
   }

   int getlowestPrice() const {
       return lowestPrice;
   }

   int gethighestPrice() const {
       return highestPrice;
   }
};

the method will be called by this line of code Prices prices = lowestNHighestPrices(prices);

I am not entirely sure of the syntax, is there a keyword of some sort I can use with the getter methods so that I can obtain the highest and lowest values from the vector? Such that getLowestPrice() == 0 and getHighestPrice() == 1 ?

Answer 1

As suggested in comments, you can use std::min_element and std::max_element . The following code (with an update of the Prices class for the empty list) makes one list iteration.

class Prices {
  protected:
   int lowestPrice;
   int highestPrice;
   bool isValid;

public:
   Prices() : lowestPrice(), highestPrice(), isValid(false) {}
   Prices(const int lowestPriceIn, const int highestPriceIn)
     : lowestPrice(lowestPriceIn), highestPrice(highestPriceIn) {}
   void updateWith(int val)
     { if (!isValid) {
         lowestPrice = highestPrice = val;
         isValid = true;
       }
       else if (val < lowestPrice)
         lowestPrice = val;
       else if (val > highestPrice)
         highestPrice = val;
     }
};

Prices lowestNHighestPrices(const vector<int>& pricelist) {
  Prices result;
  for (auto val : pricelist)
    result.updateWith(val);
  return result;
}

Answer 2

If you have C++11 available (and you should), just use std::minmax_element :

Prices lowestNHighestPrices(const vector<int>& pricelist)
{
   assert( !pricelist.empty() ); // just in case
   auto res = std::minmax_element(
      pricelist.cbegin(),
      pricelist.cend()
   );
   return Prices( *res.first, *res.second );
}

Answer 3

Return a std::pair<int, int> .

std::pair<int, int> lowestNHighestPrices() const
{
   return {lowestPrice, highestPrice};
}

Answer 4

your class already has a public interface/methods to your high and low price values. returning another structure from it or using a pass by reference parameter is although a possible solution but looks pointless in this situation. and use of std::pair, another class/structure, should be preferred where more generic code is intended, such as containers, due to its abstract naming to access member variables.