Returning Multiple Values from a Function

[paulmcco]

Hello, I need to return two separate values from the following function...within the function is a loop that compares variables and is supposed to return the numeric value of the matching variables. If there are 2 "sets" of matching variables, the function needs to be able to return as many as two values...

using namespace std;
int PairReturn(int n1, int n2, int n3, int n4, int n5)
{
	int numbs[5]= {n1, n2, n3, n4, n5}, n = 5;
		
	int j=1;
	for (int i = 0; (i < n - 1); i++)
        {			
			
			for (j = i + 1; (j < n); j++)
			{
				if (numbs[i] == numbs[j]) return numbs[j];
				
			}			
				
        }	
	return (0);	
}

This function stops after finding two matching variables (a pair)...It returns the numeric value of the pair. I would like to have this function return as many as 2 numeric values if the function finds that there are two pairs. Any ideas?

[chr15chr15]

Declare an array before your function and then add any values you wish to into that. If you do this you won't need to return any values.

[paulmcco]

How do I add the values from this function into the array? The values are determined by the function...I've heard of refering to a variable but I'm not sure how to apply it into this situation...

[Galik]

That's an unusual requirement. I might have suggested that you use the std::pair object:

std::pair<int, int> PairReturn(int n1, int n2, int n3, int n4, int n5);

However, what if you only get one match?

I would be tempted to pass in a std::vector by reference and store your one or two results in that:

#include <vector>
#include <iostream>

void GetReturn(int n1, int n2, int n3, int n4, int n5, std::vector<int>& matches)
{
	int numbs[5]= {n1, n2, n3, n4, n5}, n = 5;
		
	int j=1;
	for (int i = 0; (i < n - 1); i++)
	{			
		for (j = i + 1; (j < n); j++)
		{
			if (numbs[i] == numbs[j]) matches.push_back(numbs[i]);
		}			
	}	
}

That method may also return more than 2...

int main()
{
	std::vector<int> matches;

	GetReturn(1,3,3,5,7, matches);

	for(size_t i = 0; i < matches.size(); ++i)
	{
		std::cout << "match: " << i << " = " << matches[i] << '\n';
	}
}

You might also consider passing in your numbers in a vector rather than a long list of parameteres:

void GetReturn(const std::vector<int>& numbers, std::vector<int>& matches)
{
	...
}

[chr15chr15]

To be honest i would do it with a vector because of the member functions you get with them (push_back() in particular). Vectors are very similar to arrays if you haven't used them before

#include <vector>

using namespace std;

std::vector<int> pairvalues(100);

int PairReturn(int n1, int n2, int n3, int n4, int n5)
{
	int numbs[5]= {n1, n2, n3, n4, n5}, n = 5;
		
	int j=1;
	for (int i = 0; (i < n - 1); i++)
        {			
			
			for (j = i + 1; (j < n); j++)
			{
				if (numbs[i] == numbs[j]) pairvalues.push_back(numbs[j]);//this will add the value onto the end of your vector
				
			}			
				
        }	
	return (0);	
}

[Computergeek01]

Do you know how to use a struct or a class? That would allow you to group your returned data into one object so that it could all be returned at once. http://www.cplusplus.com/doc/tutorial/classes/

Passing the values in by reference really wouldn't help you in this case since they are just regular ints.

EDIT: @ chr15chr15: Declaring the size of the vector needlessly limits it, you should not make that into a habit.

[chr15chr15]

Point noted computergeek. However can you say it needlessly limits it. Surely if there is a limit which your vector won't surpass you are just freeing up memory?

edit: i admit in this circumstance i shouldnt have wrote 100!:)

[Computergeek01]

You're micromanaging is what you are doing. It won't hurt the program in this case, but stuff like that can be difficult to unlearn, as well as give a reader the wrong impression about vectors. The key strength of the STL containers is that they manage their own dynamic memory allocation, so there is very little need to preset a size like that.

[paulmcco]

returning a struct sounds like the best solution I will work it out, thanks everyone

[3hM2Nwbp]

Sounds like this could be a job for a varardic template to me. (C++0x only, of course)

#include<list>

template<int... Integers>
std::list<int> PairReturn(void)
{
  int n = sizeof...(Integers);
  int numbs[sizeof...(Integers)] = { Integers... };
  std::list<int> pairs;
  int j = 1;
  for (int i = 0; (i < n - 1); i++)
  {			
    for (j = i + 1; (j < n); j++)
    {
      if (numbs[i] == numbs[j])
      {
        pairs.push_back(numbs[j]);
      }
    }			
  }
  return pairs;
};


#include <iostream>

int main()
{
  std::list<int> pairs = PairReturn<0, 1, 2, 2, 3, 4, 5>();
  std::list<int> morePairs = PairReturn<0, 0, 2, 4, 2, 4, 2, 4, 5, 6, 7, 8, 4, 4, 6, 19, 33, 1773>();
  for(std::list<int>::const_iterator iter = pairs.begin(); iter != pairs.end(); ++iter)
  {
    std::cout << "Pair: " << *iter << std::endl;
  }
  return 0;
}

Regards.

[LB]

Then you lose all dynamic abilities...

[3hM2Nwbp]

Hence the could.