This code executes at -3+1==0 and other similar cases?

I have written the following code:

#include<iostream>
#include<vector>
#include<algorithm>
#include<cmath>
using namespace std;
int main()
 {
    int t,n,input;
    vector<int> neg, pos;
    cin>>t;
    while(t--)
    {
        cin>>n;
        for(int i=0;i<n;i++)
        {
            cin>>input;
            if(input<0)
            neg.push_back(input);
            else
            pos.push_back(input);
        }

    sort(neg.begin(),neg.end());
    sort(pos.begin(),pos.end());

    for(int i=0;i<neg.size();i++)
    {
        for(int j=pos.size()-1;j>=0;j--)
        {
            if(neg[i]+pos[j]==0)
            cout<<neg[i]<<" "<<pos[i];
        }
        cout<<"\n";
    }

    cout<<endl;
    neg.clear();
    pos.clear();
}
return 0;
}

which is the solution to the following problem: GeeksForGeeks Problem

What I'm trying to do: Keep negative and positive integers in 2 separate vectors. I add the numbers using 2 loops. If the sum is zero for any two combinations, I print them.

The Problem: The code does something weird. It prints -3, 1 (-3+1==0 is given as true) as a combination which is wrong. Why is code acting in such a way and what is the possible solution?