Why doesn't this code work when I use cin.getline instead of cin?

My goal is to: Given a string S, of length N that is indexed from 0 to N-1, print its even-indexed and odd-indexed characters as 2 space-separated strings on a single line

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include<string.h>
using namespace std;


int main() {

        int test;
        cin>>test;
        for(int j = 0; j < test; j++){

            char str[10000];
            cin.ignore();
            cin.getline(str,9999);
            //cin>>str;

            for( int i = 0; i < strlen(str); i++)
            {
                if(i % 2 == 0)  
                    cout<<str[i];   
            }
            cout <<" ";
            for(int i = 0; i < strlen(str); i++)
            {
                if((i % 2 != 0))
                    cout<<str[i];    
            }

            cout << endl;  

        }

    return 0;
}

The above code gives me output as :
Hce akr
ak n

for the given input of :
2
Hacker
Rank

But when I use cin>>str instead of the cin.ignore and cin.getline I get the correct expected output

Hce akr
Rn ak