View Compilation Error

0_0_19939524_24137.cpp:14:26: error: expected initializer before '+' token
 __int64 dx(int j,int k)  +-
                          ^
0_0_19939524_24137.cpp: In function 'int main()':
0_0_19939524_24137.cpp:36:79: error: 'dx' was not declared in this scope
             while(head<tail&&f(q[head+1],q[head])<=sum[i]*dx(q[head+1],q[head]))++head;  
                                                                               ^
0_0_19939524_24137.cpp:38:63: error: 'dx' was not declared in this scope
             while(head<tail&&f(i,q[tail])*dx(q[tail],q[tail-1])<=f(q[tail],q[tail-1])*dx(i,q[tail]))--tail;  
                                                               ^