Fine tune without using pointers - c++

Question

** To print repeated elements from an user defined array
//print repeated elements from an array
#include<iostream>
using namespace std;
int main()
{
int p,n;
cout<<"enter no. of elements in array: "<<endl;
cin>>n;
int a[n],b[n];
int z=0;
cout<<"enter elements of array:"<<endl;
for(int i=0;i<n;i++)
{
cin>>a[i];
}
for(int j=0;j<n;j++)
{
for(int k=j;k<=n;k++)
{
if(j==k)
{
continue;
}
else if(a[j]==a[k])
{
b[z]=a[j];
++z;
a[k]=a[k+1]; //deleting the array element which repeats
a[n-1]=0; //settng last element as 0
--n; //reducing the size of array
break;
}
int d=z;
if(b[j]==b[k])
{
b[j]=b[j+1];
b[n-1]=0;
n--;
}
}
}
if(z==0)
{
cout<<"No Elemnts in the array is repeated"<<endl;
}
else
{
cout<<"repeated elements are: "<<endl;
for(p=0;p<z;p++)
{
cout<<b[p]<<" ";
}
}
return 0;
}
How to fine tune this program so as it displays correct output? When we enter 3 similar elements it repeats itself twice and also has problem reading the last element.
Thanks

Answer 1

You should rewrite your algorithm. Something like that should work:
std::vector<int> a;
/* fill a */
std::sort(a.begin(), a.end());
std::vector<int> unique_elements;
std::unique_copy(a.begin(), a.end(), std::back_inserter(unique_elements));
std::vector<int> b;
std::copy_if(unique_elements.begin(), unique_elements.end(), std::back_inserter(b), [&](int n)
{
return std::count(a.begin(), a.end(), n) >= 2;
});