don't use certain STL functions

some functions defined in <cmath>, as well as std::to_string aren't available on GNU's STL for some platforms, e.g. Android

linux/main.cpp

@@ -12,6 +12,8 @@
 #include <getopt.h>
 #include <fstream>
 #include <sstream>
+#include <cstdlib>
+#include <cstdio>
 
 namespace {