7.29.cpp

/*
 * Exercise 7.29: Revise your Screen class so that move, set, and display
 * functions return Screen and check your prediction from the previous
 * exercise.
 *
 * By Faisal Saadatmand
 */

#include <iostream>
#include <string>

class Screen {
	public:
		using pos = std::string::size_type;

		Screen() = default;
		Screen(pos ht, pos wd, char c) : height(ht), width(wd),
		                                 contents(ht * wd, c) {}
		Screen(pos ht, pos wd) : height(ht), width(ht),
		                         contents(ht * wd, ' ') {}
		// members
		Screen display(std::ostream &os)
		               { do_display(os); return *this; }
		const Screen display(std::ostream &os) const
		               { do_display(os); return *this; }
		Screen set(char);
		Screen set(pos, pos, char);
		char get() const            // get the character at the cursor
		    { return contents[cursor]; }         // implicitly inline
		inline char get(pos ht, pos wd) const;   // explicitly inline
		Screen move(pos r, pos c);   // can be made inline later

	private:
		void do_display(std::ostream &os) const {os << contents;}
		pos cursor{0};
		pos height{0};
		pos width{0};
		std::string contents;
};


inline Screen Screen::set(char c)
{
	contents[cursor] = c;     // set the new value at the current cursor location
	return *this;             // return this object as an lvalue
}

inline Screen Screen::set(pos r, pos col, char ch)
{
	contents[r * width + col] = ch;   // set specified location to given value
	return *this;
}

inline Screen Screen::move(pos r, pos c)
{
	pos row = r * width;      // compute the row location
	cursor = row + c;         // move cursor to the column within that raw
	return *this;             // return this object as an lvalue
}

char Screen::get(pos r, pos c) const // declared as inline in the class
{
	pos row = r * width;       // compute row location
	return contents[row + c];  // return character at the given column
}

int main()
{
	Screen myScreen(5, 5, 'X');
	myScreen.move(4, 0).set('#').display(std::cout);
	std::cout << "\n";
	myScreen.display(std::cout);
	std:: cout << "\n";
	return 0;
}