feat: implement CPP05 C++20 card

src/task01/counter.cpp

@@ -0,0 +1,4 @@
+#include "counter.hpp"
+Counter::Counter(int start) : value_{start} {}
+void Counter::increment() { ++value_; }
+int Counter::value() const { return value_; }

src/task01/counter.hpp

@@ -0,0 +1,2 @@
+#pragma once
+class Counter { public: explicit Counter(int start); void increment(); int value() const; private: int value_; };

src/task01/main.cpp

@@ -0,0 +1,3 @@
+#include "counter.hpp"
+#include <iostream>
+int main() { Counter counter{2}; counter.increment(); std::cout << "counter=" << counter.value() << '\n'; }

src/task02/main.cpp

@@ -0,0 +1,9 @@
+#include <iostream>
+class Account {
+public:
+    explicit Account(int balance) : balance_{balance} {}
+    bool deposit(int amount) { if (amount <= 0) return false; balance_ += amount; return true; }
+    int balance() const { return balance_; }
+private: int balance_;
+};
+int main() { Account account{10}; const bool accepted = account.deposit(5); const bool rejected = !account.deposit(-2); std::cout << "accepted=" << accepted << " rejected=" << rejected << " balance=" << account.balance() << '\n'; }

src/task03/main.cpp

@@ -0,0 +1,3 @@
+#include <iostream>
+class Rectangle { public: Rectangle(int width, int height) : width_{width}, height_{height} {} int area() const { return width_ * height_; } void scale(int factor) { width_ *= factor; height_ *= factor; } private: int width_; int height_; };
+int main() { Rectangle rectangle{6, 4}; const int before = rectangle.area(); rectangle.scale(2); std::cout << "area=" << before << " scaled=" << rectangle.area() << '\n'; }