continue aiming for C++98

I will give up if this takes too long and go to C++11

cplusplus/p0004.cpp

@@ -13,6 +13,7 @@ Find the largest palindrome made from the product of two 3-digit numbers.
 #ifndef EULER_P0004
 #define EULER_P0004
 #include <algorithm>
+#include <cstdio>
 #include <iostream>
 
 unsigned int p0004() {