What can't I make a call in global scope?

[孙宗君]

Why the following code is illegal?


#include <iostream>
#include <vector>

vector<int > vi;

vi.push_back(10); //why this line is illegal?
int ii = vi.at(0); // this line is legal??

int main()
{
  return 0;
}


Appreciation for your kindly help/

Zongjun