unknown bug causing program to return weird symbols

I wrote a very basic program to separate vowels from a input string. The program is separating vowels but also returning weird symbols/letters!

I seriously can't find why it is happening! help!

output >>

aoeeo x ╘E⌡óì

It generates different letters(?) everytime i run it!

code >>

#include <iostream>
#include <vector>
#include <string>
using namespace std;

int main(){
  string input = "stackoverflow";
  vector<char>  vowels = {'a','e','i','o','u'};
  vector<char> result;

  for(int i = 0 ; i < input.size() ; i++){
    for(int j = 0; j < vowels.size(); j++){
      if(input[i] == vowels[j]){
      result.push_back(input[i]);
      }
    }
      if (input[i] == 'u' || input[i] == 'e') {
        result.push_back(input[i]);
      }
  }

  for(int i = 0 ; i < input.size() ; i++){
    cout << result[i];
  }

  return 0 ;
}