--- book.cc
+++ book.cc
@@ -28,6 +28,7 @@
 #include <vector>
 #include <iostream>
 #include <stdexcept>
+#include <cstdlib>
 
 #ifdef _
 #undef _
--- game.cc
+++ game.cc
@@ -37,6 +37,7 @@
 #include <sys/stat.h> 
 #include <unistd.h>
 #include <fcntl.h>
+#include <cstdlib>
 
 #ifdef _
 #  undef _
--- log_proc.h
+++ log_proc.h
@@ -25,6 +25,7 @@
 #include <string>
 #include <fstream>
 #include <iomanip>
+#include <cstdlib>
 
 #include "board.h"
 #include "order.h"