More idiomatic C++

Drop endl which is not newline and the return 0 that is implicit.

c/c++.cpp

@@ -1,9 +1,6 @@
 #include <iostream>
 
-using namespace std;
-
 int main()
 {
-   cout << "Hello World" << endl;
-   return 0;
+   std::cout << "Hello World\n";
 }