vs2013 未定义标识符random？？？明明定义了，求教

#include
using namespace std;
#include
#include
#include
#define random(x) (random()%x)

class Elem
{
public:
int dotime;
Elem *next;
Elem(){
srand((int)time(0));
dotime = random(30);
next = NULL;
}
};
class ElemQueue
{
Elem *front;
Elem *rear;
ElemQueue(){
front = new Elem();
rear = new Elem();
front->next = rear;
}
};
int main()
{
Elem *elem = new Elem();
cout << elem->dotime << endl;
system("pause");
return 0;
}

1>c:\users\pangjingyu\documents\visual studio 2013\projects\project1\project1\银行排号系统.cpp(15): error C3861: “random”: 找不到标识符

哪里定义了。#define random(x) (random()%x)，里面那个random没有声明。