The out put console shows nothing

This is the program of removing all the vowels from the given string. My code does not show any output in the console.

#include <bits/stdc++.h>
using namespace std;
int isVowel(char ch)
{
    if(ch=='a'||ch=='e'||ch=='i'||ch=='o'||ch=='u'||ch=='A'||ch=='E'||ch=='I'||ch=='O'||ch=='U')
    return 1;
    else 
    return 0;
}

int main()
{
    string str,str1;
    getline(cin,str);
    int index=0;
    for(int i=0;str[i]!='\0';i++)
    {
        if(isVowel(str[i])==0)
        str1[index++]=str[i];
    }
    str1[index]='\0';
    //strcpy(str,str1);
    cout<<str1;

    return 0;
}

This is the code.