View Compilation Error

0_0_17288193_7814.c:79:1: error: expected identifier or '(' before '/' token
 // ((P1Pi cross P1Pj)>0) or ((P1Pi cross P1Pj)=0) and (|p1pi| > |p1pj|)
 ^
0_0_17288193_7814.c: In function 'main':
0_0_17288193_7814.c:109:58: error: 'cmp' undeclared (first use in this function)
         qsort(points + 1, (size_t) n - 1, sizeof(Point), cmp);
                                                          ^
0_0_17288193_7814.c:109:58: note: each undeclared identifier is reported only once for each function it appears in
0_0_17288193_7814.c:123:9: error: expected expression before '/' token
         // ans = ans + 2*pi*l
         ^