Why is string declared 'globally' different than declared 'locally'?

Problem : Given a string S, of length N that is indexed from 0 to N-1 , print its even-indexed and odd-indexed characters as space-separated strings on a single line i.e. if String is Hacker Output should be Hce akr.I wrote this code...

#include 
using namespace std;

int main() {
    int T;
    cin>>T;
    string str;
      string evenStr;
      string oddStr;
    for(int i=1; i<=T; i++)
    { 
      cin>>str;
      for(int j=0;j

For input T=2 and two strings "Hacker" "Rank"...this code Outputs "Hce akr" "HceRn akrak"But this code prints the correct result...Why?

#include 
using namespace std;

int main() {
    int T;
    cin>>T;

    for(int i=1; i<=T; i++)
    { string str;
      string evenStr;
      string oddStr;
      cin>>str;
      for(int j=0;j

For input T=2 and two strings "Hacker" "Rank"... Correct Output: "Hce akr" " Rn ak"