no member named 'array' in namespace 'std' - c++

Question

I am learning C++ right now and i get this somewhat weird error.
The Code is as follows:
#include <iostream>
#include <array>
using std::cout;
using std::endl;
using std::ostream;
using std::array;
template <typename T, size_t dim>
ostream& operator<<(ostream& os, const array<T,dim>& a) {
os << "[ ";
for (auto n : a)
os << n << " ";
os << "]";
return os;
}
int main()
{
cout << endl << "--- " << __FILE__ << " ---" << endl << endl;
array<int,3> a1 { 2,3,5 }; // (A)
array<int,0> a2 { }; // (B)
array<int,2> a3 { 1 }; // (C)
// array<int> x1 { 1, 2, 3 }; // (D)
// array<int,3> x2 { 1,2,3,4 };
array<int,3> a4 = { 1,2,3 }; // (E)
array<int,3> a5 { { 4,5,6 } }; // (F)
cout << "01| a1=" << a1 << endl;
cout << "02| a2=" << a2 << endl;
cout << "03| a3=" << a3 << endl;
cout << "04| a4=" << a4 << endl;
cout << "05| a5=" << a5 << endl;
cout << endl << "--- " << __FILE__ << " ---" << endl << endl;
return 0;
}
My IDE (Visual Studio Code) shows me the error, although the code is compiling and working.
Here is the makefile provided by our Prof.
# compiler settings
CXX = g++-7
# CXX = clang++
CXXFLAGS = -ansi -pedantic -Wall -Wextra -Wconversion -pthread -std=c++17
LDFLAGS = -lm
# collect files
CXXEXAMPLES = $(shell find . -name '*.cpp' -print -type f)
CXXTARGETS = $(foreach file, $(CXXEXAMPLES), ./out/$(file:.cpp=.out))
# build them all
all: $(CXXTARGETS)
out/%.out: %.cpp
$(CXX) $(CXXFLAGS) $< $(LDFLAGS) -o $#
clean:
rm out/*
I use Ubuntu 16.04 and thought it might be a compiler problem, so I changed "CXX" to "CXX = g++-7", because we were recommended to use g++ Version 7 but it didn't helped.
On typing "g++ -v" it shows that my gcc is version 5.5.0, but typing "apt list -installed" shows that g++-7 is installed.
I did not find any solution on the internet as most similar problems often revolved around missing includes.
VS Code also does not recognize some types of variable definitions like
"int n{1}"
It also complains about the "use of undeclared identifier" on the lines (A) to (E)
I assume the problem lies within the VS Code compiler using a different/old syntax recognition. But I don't know how to change that.