added drill18 for chapter13

Author: trapperdot00

Chapter13/README.md

@@ -55,3 +55,6 @@ Give `Person` a constructor initializing `name` and `age`.
 
 ## [Drill 17](drill/17)
 Make the representation of `Person` private, and provide `const` member functions `name()` and `age()` to read the name and age.
+
+## [Drill 18](drill/18)
+Modify `>>` and `<<` to work with the redefined `Person`.

Chapter13/drill/18/Person.cpp

@@ -0,0 +1,13 @@
+#include "Person.h"
+
+std::istream& operator>>(std::istream& is, Person& rhs) {
+	std::string name;
+	int age = 0;
+	if (is >> name >> age)
+		rhs = Person{name, age};
+	return is;
+}
+
+std::ostream& operator<<(std::ostream& os, const Person& rhs) {
+	return os << rhs.name() << ' ' << rhs.age();
+}

Chapter13/drill/18/Person.h

@@ -0,0 +1,23 @@
+#ifndef PERSON_H
+#define PERSON_H
+
+#include <string>
+#include <iostream>
+
+class Person {
+public:
+	Person() {}
+	Person(const std::string& s, int i)
+		: n{s}, a{i} {}
+
+	std::string name() const { return n; }
+	int age() const { return a; }
+private:
+	std::string n;
+	int a;
+};
+
+std::istream& operator>>(std::istream&, Person&);
+std::ostream& operator<<(std::ostream&, const Person&);
+
+#endif

Chapter13/drill/18/main.cpp

@@ -0,0 +1,10 @@
+#include "Person.h"
+
+#include <iostream>
+
+int main() {
+	Person p;
+	std::cout << "Enter person: ";
+	if (std::cin >> p)
+		std::cout << p << '\n';
+}