support bazel complie this project and format code.

practical_exercises/key_exercises/output.cpp

@@ -0,0 +1,19 @@
+/* 输出格式.cpp */
+#include <iomanip>
+#include <iostream>
+using namespace std;
+
+int main(int argc, char const *argv[]) {
+  char s[20] = "this is a string";
+  double digit = -36.96656;
+  cout << setw(30) << left << setfill('*') << s << endl;
+  cout << dec << setprecision(4) << digit << endl;
+  cout << dec << 15 << endl;
+  // setbase(int x)设置进制后，后面所有操作都是按照这个进制来计算！
+  cout << setbase(10) << 15 << endl;
+  //四舍五入,并保留2位有效数组
+  float x = 6.6937;
+  cout << float(int(x * 1000 + 0.5) / 1000.0) << endl;
+  
+  return 0;
+}