switching to use printf instead of "cout <<"

src/hello-world.cpp

@@ -1,10 +1,7 @@
-#include <iostream>
-
-using namespace std;
-
+#include <cstdio>
 
 int main()
 {
-    cout << "Hello World!\n";
+    printf("Hello World!\n");
     return 0;
 }