How to Merge two vectors

[BatCity93]

can someone help me out here, say i have two vectors, one equals [1,2,3] and the other equals [9,8,7],what i am trying to do is make it so that the program prints out [1 9 2 8 3 7]. if anyone can point me onto the right direction i would greatly appreciate it. thank you who comment in advance.

#include <iostream>
#include <algorithm> 
#include <vector>

using namespace std;

vector<int> append(vector<int> a, vector<int> b)
{
    int n = a.size();
    int m = b.size();
    vector<int> c(n + m);
    int i;

    for (i = 0; i < n; i++)
        c[i] = a[i];

    for (i = 0; i < m; i++)
        c[n + i] = b[i];

    return c;
}

vector<int> merge(vector<int> a, vector<int> b) 
{
	int n = a.size();
    int m = b.size();
    vector<int> c(n + m);
    int i;

    for (i = 0; i < n; i++)
        c[i] = a[i];

    for (i = 0; i < m; i++)
        c[n + i] = b[i];

    return c;
}

vector<int> merge_sorted(vector<int> a, vector<int> b)
{

	int n = a.size();
    int m = b.size();
    vector<int> c(n + m);
    int i;

    for (i = 0; i < n; i++)
        c[i] = a[i];

    for (i = 0; i < m; i++)
        c[n + i] = b[i];

    return c;
}

int main()
{
    cout << "Please enter a set of numbers, insert -1 when done.\n";
    vector<int>a;
    bool more = true;
    while (more)
    {
        int n;
        cin >> n;
        if (n == -1)
            more = false;
        else
            a.push_back(n);
    }


    cout << "Please enter another set of numbers, insert -1 when done.\n";
    vector<int>b;
    more = true;
    while (more)
    {   
        int m;
        cin >> m;
        if (m == -1)
            more = false; 
        else 
            b.push_back(m);
    }

    vector<int>d = append(a,b);
    {
  
        int i;
		cout << "Appended: ";
        for (i= 0; i < d.size(); i++)

       cout << d[i] << " ";
	   cout << "\n";
	}

	vector<int>r = merge(a,b);
	{
		//int i;

	    cout << "Merged: ";

	   
		//for (i = 0; i < r.size();++i)
		/*{
			merge (a.begin(), a.end(), b.begin(), b.end(), r.begin());
		}*/
		//cout << r[i] << " ";

		sort (a.end(),a.begin());
		sort (b.end(),b.begin());
		merge (a.end(),a.begin(),b.end(),b.begin(),r.begin());

		 for (std::vector<int>::iterator it=r.begin(); it!=r.end(); ++it)
    std::cout << ' ' << *it;

	    cout << "\n";
	}
    vector<int>z = merge_sorted(a,b);
	{

	a.insert( a.end(), b.begin(), b.end() );
	sort( a.begin(), a.end() );

	cout << "Sorted: ";

	for (vector<int>::iterator it = a.begin(); it != a.end(); ++it)
    cout << *it << " ";
	cout << "\n";
	} 
}

[JLBorges]

> one equals [1,2,3] and the other equals [9,8,7],
> what i am trying to do is make it so that the program prints out [1 9 2 8 3 7].

To avoid confusion, you should not call that operation merge.

#include <vector>
#include <algorithm>
#include <iostream>

std::vector<int> interleave( const std::vector<int>& a, const std::vector<int>& b )
{
   std::vector<int> result ;

   auto m = std::min( a.size(), b.size() ) ;

   for( std::size_t i=0 ; i<m ; ++i )
   {
       result.push_back(a[i]) ;
       result.push_back(b[i]) ;
   }
   if( m < a.size() ) result.insert( result.end(), a.begin()+m, a.end() ) ;
   if( m < b.size() ) result.insert( result.end(), b.begin()+m, b.end() ) ;

   return result ;
}


int main()
{
    for( int v : interleave( {0,1,2,3,4,5}, {6,7,8,9} ) ) std::cout << v << ' ' ;
    std::cout << '\n' ;
}

http://liveworkspace.org/code/1JkyNQ$0