compiling error Programming Principles and Practice using c++

I'm working on the drill for chapter 6 in Bjarne Stroustrup's c++ book and i keep getting this error when i try to compile my code. error: ‘keep_window_open’ was not declared in this scope keep_window_open(); I tried looking through the book, but i can't seem to figure out how to fix the problem. I'm not sure if I have to include something. Any sort of help or tips are appreciated! Thanks!

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#ifndef H112
#define H112 201004L
#include<iostream>
#include<fstream>
#include<sstream>
#include<cmath>
#include<cstdlib>
#include<string>
#include<list>
#include<vector>
#include<algorithm>
#include<stdexcept>



using namespace std;



class Token {
public:
    char kind;        // what kind of token
    double value;     // for numbers: a value 
    Token(char ch)    // make a Token from a char
        :kind(ch), value(0) { }
    Token(char ch, double val)     // make a Token from a char and a double
        :kind(ch), value(val) { }
};

class Token_stream {
public:
    Token_stream();   // make a Token_stream that reads from cin
    Token get();      // get a Token (get() is defined elsewhere)
    void putback(Token t);    // put a Token back
private:
    bool full;        // is there a Token in the buffer?
    Token buffer;     // here is where we keep a Token put back using putback()
};




// The constructor just sets full to indicate that the buffer is empty:
 Token_stream::Token_stream()
 :full(false), buffer(0)    // no Token in buffer
 {
 }




// The putback() member function puts its argument back into the Token_stream's buffer:
 void Token_stream::putback(Token t)
 {
     if (full) cerr<<("putback() into a full buffer")<<"\n";
         buffer = t;       // copy t to buffer
             full = true;      // buffer is now full
             }





Token Token_stream::get()
{
if (full) {       // do we already have a Token ready?
        // remove token from buffer
        full=false;
        return buffer;
          }

    char ch;
    cin >> ch;    // note that >> skips whitespace (space, newline, tab, etc.)

    switch (ch) {
    case ';':    // for "print"
    case 'q':    // for "quit"
    case '(': case ')': case '+': case '-': case '*': case '/':
        return Token(ch);        // let each character represent itself
    case '.':
    case '0': case '1': case '2': case '3': case '4':
    case '5': case '6': case '7': case '8': case '9':
        {
            cin.putback(ch);         // put digit back into the input stream
            double val;
            cin >> val;              // read a floating-point number
            return Token('8',val);   // let '8' represent "a number"
        }
    default:
        cerr<<("Bad token")<<"\n";
    }
}


Token_stream ts;        // provides get() and putback()



double expression();    // declaration so that primary() can call expression()




// deal with numbers and parentheses
 double primary()
 {
     Token t = ts.get();
     switch (t.kind) {
     case '(':    // handle '(' expression ')'
        {
                double d = expression();
                t = ts.get();
                if (t.kind != ')') cerr<<("')' expected")<<"\n";
                return d;
        }
     case '8':            // we use '8' to represent a number
        return t.value;  // return the number's value
     default:
          cerr<<("primary expected")<<"\n";
                    }
 }




// deal with *, /, and %
 double term()
 {
     double left = primary();
         Token t = ts.get();        // get the next token from token stream

         while(true) {
                switch (t.kind) {
                case '*':
                        left *= primary();
                        t = ts.get();
                        break;
                case '/':
                        {
                        double d = primary();
                        if (d == 0) cerr<<("divide by zero")<<"\n";
                        left /= d;
                        t = ts.get();
                        break;
                        }
                default:
                        ts.putback(t);     // put t back into the token stream
                        return left;
        }
    }
}





// deal with + and -
double expression()
{
        double left = term();      // read and evaluate a Term
        Token t = ts.get();        // get the next token from token stream

        while(true) {
                switch(t.kind) {
                case '+':
                        left += term();    // evaluate Term and add
                        t = ts.get();
                        break;
                case '-':
                        left -= term();    // evaluate Term and subtract
                        t = ts.get();
                        break;
                default:
                        ts.putback(t);     // put t back into the token stream
                        return left;       // finally: no more + or -: return the answer      
                }
        }
}




int main()
{
        try
        {
         double val = 0;
         while (cin) {
                Token t = ts.get();

                if (t.kind == 'q') break; // 'q' for quit
                if (t.kind == ';')        // ';' for "print now"
                        cout << "=" << val << '\n';
                else
                        ts.putback(t);
                val = expression();
                }
                keep_window_open();
        }
        catch (exception& e) {
                cerr << "error: " << e.what() << '\n';
                        keep_window_open();
                return 1;
        }
        catch (...) {
                cerr << "Oops: unknown exception!\n";
                        keep_window_open();
                return 2;
        }
}

#endif
i already included that at the top of my program as you can see. unless you are referring to something else? im not sure..
I don't see #include "std_lib_facilities.h" in your code
it gave me this error when i tried to compile it after i included that

fatal error: std_lib_facilities.h: No such file or directory
#include "std_lib_facilities.h"
download the file, add it to your project (so you may use a relative path, you may also copy it to the project directory), and include it.
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