Encoding Message(cpp)

#include <iostream>
using namespace std;

int main()
{
    int T;
    cin>>T;
    while(T--)
    {
        int N;
        cin>>N;
        string S;
        cin>>S;
        int i=0;
        if(N%2==0)
        {
            while(i<N)
            {
                char temp=S[i+1];
                S[i+1]=S[i];
                S[i]=temp;
                i+=2;
            }
        }else
        {
            i=0;
            while(i<N-1)
            {
                char temp=S[i+1];
                S[i+1]=S[i];
                S[i]=temp;
                i+=2;
            }
        }
        for(int i=0;i<N;i++)
        {
            int a='z'-S[i];
            S[i]='a'+a;
        }
        cout<<S<<endl;
    
        }

    return 0;
}