Why does this simple code not work?

Question

I just want to print the vector. Does cout not support double? If it doesn't, this is not the error. I have the same problem with strings. Thanks!

#include <iostream>
#include <vector>
#include <math.h>
using namespace std;

int main() {
std::vector <double> grad;
grad.push_back=1;
grad.push_back =2;

cout<<grad.at(0)<<endl;
cout<<grad.at(1);
return 0;
}

Answer 1

grad.push_back(1);