#include <iostream.h>

int main()
{
     cout<<"Do you want a random number?(Y/N)"<<endl;
     char chAnswer;
     cin>>chAnswer;
     if (chAnswer == 'N')
         goto DONE;
     else
     {
        int nRandom=rand();
        cout<<"The random number created by rand()  function is "<<nRandom<<endl;
     }
    DONE:
        cout<<"Thank you !!"<<endl;
        return 0;
}   

rand()需要调用头文件stdlib.h

楼上正解~，不同的函数要调用不同的头文件