I wrote the exact same code that has in my c++ textbook but it doesn't work

#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<cmath>
using namespace std;
inline void keep_window_open() { char ch; cin >> ch; }

after I wrote that code I am getting both the 2019, and the 1120 errors and I cannot undrstand what is going on.