View Compilation Error

0_0_25287631_22302.cpp:10:1: error: expected ',' or ';' before 'int'
 int sgn(db x)
 ^
0_0_25287631_22302.cpp: In function 'bool _cmp(Point, Point)':
0_0_25287631_22302.cpp:81:16: error: 'sgn' was not declared in this scope
     if (sgn(tmp)>0) return true;
                ^
0_0_25287631_22302.cpp: In function 'void Graham(int)':
0_0_25287631_22302.cpp:119:91: error: 'sgn' was not declared in this scope
         while (top>1&&sgn((lis[Stack[top-1]]-lis[Stack[top-2]])^(lis[i]-lis[Stack[top-2]]))<=0) top--;
                                                                                           ^