support bazel complie this project and format code.

practical_exercises/key_exercises/operator_circle.cpp

@@ -0,0 +1,25 @@
+/* 重载圆括号的时钟.cpp */
+#include <iostream>
+using namespace std;
+class Time {
+private:
+  int hh, mm, ss;
+
+public:
+  Time(int h = 0, int m = 0, int s = 0) : hh(h), mm(m), ss(s) {}
+  void operator()(int h, int m, int s) {
+    hh = h;
+    mm = m;
+    ss = s;
+  }
+  void ShowTime() { cout << hh << ":" << mm << ":" << ss << endl; }
+};
+int main() {
+  Time t1(12, 10, 11);
+  t1.ShowTime();
+  t1.operator()(23, 20, 34);
+  t1.ShowTime();
+  t1(10, 10, 10);
+  t1.ShowTime();
+  
+}