/in/foo.cc: In function 'int main()':
/in/foo.cc:31:6: error: 'i' was not declared in this scope
  for(i=0;i<n;i++)
      ^
/in/foo.cc:36:2: error: 'start' was not declared in this scope
  start=0;
  ^~~~~
/in/foo.cc:53:21: error: 'num' was not declared in this scope
    cout<<"次数:"<<num<<endl;
                     ^~~
/in/foo.cc:29:17: warning: unused variable 'strat' [-Wunused-variable]
  int n,a[N],key,strat,end,mid;
                 ^~~~~