Invalid operands to binary expression ('std::__1::ostream' (aka 'basic_ostream

I'm new to c++ so the solution may be obvious, but I'm attempting to cast ASCII numbers to their corresponding letters of the alphabet using a sentinel controlled loop. The compiler gives me the error "Invalid operands to binary expression ('std::__1::ostream' (aka 'basic_ostream') and 'vector')" next to cout. I'm using XCode. Any help would be much appreciated.

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

int main(){
    int num;
    char intermediary;
    vector<char> Letters;
    cin>>num;
    while (num!= -1){
        intermediary=char(num);
        Letters.push_back(intermediary);
        cin>>num;
    }
    cout<<Letters<<endl;
    return 0;
}