support bazel complie this project and format code.

practical_exercises/10_day_practice/day7/index_parentheses/BUILD

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+# please run `bazel run //practical_exercises/10_day_practice/day7/subscript_operator:example`
+
+load("@rules_cc//cc:defs.bzl", "cc_binary")
+
+cc_binary(
+    name = "exexampleample1",
+    srcs = ["example.cpp"],
+)

practical_exercises/10_day_practice/day7/index_parentheses/example.cpp

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+/* []与() 运算符重载 */
+#include <iostream>
+using namespace std;
+class X {
+public:
+  int operator()(int i = 0) {
+    cout << "X::operator(" << i << ")" << endl;
+    return i;
+  };
+  int operator()(int i, int j) {
+    cout << "X::operator(" << i << "," << j << ")" << endl;
+    return i;
+  };
+  int operator[](int i) {
+    cout << "X::operator[" << i << "]" << endl;
+    return i;
+  };
+  int operator[](char *cp) {
+    cout << "X::operator[" << cp << "]" << endl;
+    return 0;
+  };
+};
+int main(void) {
+  X obj;
+  int i = obj(obj(1), 2);
+  int a = obj[i];
+  int b = obj["abcd"];
+  cout << "a=" << a << endl;
+  cout << "b=" << b << endl;
+  
+}