Cannot access member functions of vector<int> - c++

Question

I've been attempting to figure out this bug for about an hour now. It's probably a really obvious syntax thing I'm overlooking. This is my first C++ project, and I don't have a good handle on the structure of the language.
Here's my header file:
#pragma once
#include <vector>
class BoardState
{
private:
std::vector<int> numbers;
int SIZE;
public:
BoardState();
std::vector<int> getState();
bool isZero();
};
And here's the implementation, in a separate file:
#include "BoardState.h"
BoardState::BoardState(){
SIZE = 4;
numbers.push_back(1);
numbers.push_back(3);
numbers.push_back(5);
numbers.push_back(7);
}
std::vector<int> BoardState::getState() { return numbers; }
bool BoardState::isZero() {
for (int i = 0; i < numbers.size(); i++) {
if (numbers[i] != 0) { return false; }
}
return true;
}
This code is really simple, so I have no clue what could be going wrong to produce the errors. However, on every method call, push_back and size, I am getting errors, saying that class "std::vector<int, allocator>" has no member "method_name_here".
My background is Java, so my first thought was that I wasn't able to call these methods because numbers is not initialized. However, any attempt I made to initialize numbers in the header file resulted in an error as well. I tried std::vector<int> numbers = { 1,3,5,7 };, I tried std::vector<int> numbers(4,0);, I even tried creating an array and constructing the vector from that. Not only did all those attempts cause errors, they also didn't fix the method calls either.
What am I missing? Do I need to initialize the vector, or is what I have in the header file enough? Any advice would be helpful here, since I can't find anything online about similar errors. I've even copy-pasted code from StackOverflow answers about similar problems, and that produced errors as well.
EDIT: I've pared down the code as much as possible while keeping the error:
#include <vector>
class BoardState
{
std::vector<int> numbers;
BoardState() { numbers.push_back(1); }
int getSize() {
int i = numbers.size();
return i;
}
};
On the line numbers.push_back(1);, my compiler underlines the token "push_back", and highlighting it reads:
class "std::vector<int, allocator>" has no member "push_back"
On the line int i = numbers.size();, the token "size" is underlined, and the error reads:
class "std::vector<int, allocator>" has no member "size"
I still have no clue what's going on.
Edit 2: Put the method calls into a constructor and a function. This changed the error message associated with push_back().
Edit 3: I have discovered something very disconcerting. This code works perfectly fine in a different compiler. I copy-pasted in the exact code from Edit 1 and it ran with no issues. I think the problem must be with Visual Studio rather than the actual code. Thank you all for helping me out with this. I think I'm just going to switch to a different compiler and hope for the best.
Edit 4: Just to prove to pm100 that my code is exactly as I've said, here's a screenshot from visual studio.
Here it is.
Aside from the main method, this is character-for-character what I've put in this question. I have a guess as to why this doesn't work, though. I modified my version of Visual Studio 2019 to run .386 assembly code for a college class. While I think I followed the guide to do that without affecting anything else, it may have screwed up parts of the C++ compiler.

Answer 1

I suggest that you could select Tools->Import and Export Settings->Reset all settings-> Visual C++ to restore the default settings.
If it does not work, you could reinstall VS.