Poj3348 Cows convex hull + Polygon Area Water question

/* Poj3348 Cows convex bag + Polygon Area Water question floor rounded down, returns double */# include <stdio. h> # include <math. h ># include <algorithm> using namespace std; const double eps = 1e-8; struct point {double x, y ;}; int n; point dian [10000 + 10], zhan [10000 + 10]; //////////////////////////////////////// /// // point * mo_dian; double mo_distance (point p1, point p2) {return sqrt (p1.x-p2.x) * (p1.x-p2.x) + (p1.y-p2.y) * (p1.y-p2.y ));} double mo_xmult (poin T p2, point p0, point p1) // p1 returns a negative value on the left of p2, and returns a positive {return (p1.x-p0.x) * (p2.y-p0.y) on the right) -(p2.x-Snapshot x) * (p1.y-Snapshot y);} bool mo_ee (double x, double y) {double ret = x-y; if (ret <0) ret =-ret; if (ret <eps) return 1; return 0;} bool mo_gg (double x, double y) {return x> y + eps ;} // x> y bool mo_ll (double x, double y) {return x <y-eps;} // x <y bool mo_ge (double x, double y) {return x> y-eps;} // x> = y bool mo_le (double x, Double y) {return x <y + eps;} // x <= y bool mo_cmp (point a, point B) // The first order {if (mo_ee (. y, B. y) return mo_ll (. x, B. x); return mo_ll (. y, B. y);} bool mo_cmp1 (point a, point B) // second sort {double len = mo_xmult (B, mo_dian [0], a); if (mo_ee (len, 0.0) return mo_ll (mo_distance (mo_dian [0], a), mo_distance (mo_dian [0], B); return mo_gg (len, 0.0 );} int mo_graham (int n, point * dian, point * stk) {int I, t Op = 1; mo_dian = dian; sort (mo_dian, mo_dian + n, mo_cmp); sort (mo_dian + 1, mo_dian + n, mo_cmp1 ); stk [0] = mo_dian [0]; stk [1] = mo_dian [1]; for (I = 2; I <n; ++ I) {while (top> 0 & mo_xmult (mo_dian [I], stk [top-1], stk [top]) <= 0) -- top; stk [++ top] = mo_dian [I];} return top + 1;} double mo_area_polygon (point * dian, int n) {int I; point yuan; yuan. x = yuan. y = 0; double ret = 0; for (I = 0; I <n; ++ I) {ret + = mo_xmult (dian [(I + 1) % n], yuan, dian [I]);} if (re T <0) ret =-ret; return ret/2;} // int main () {int I; while (scanf ("% d ", & n )! = EOF) {for (I = 0; I <n; ++ I) {scanf ("% lf", & dian [I]. x, & dian [I]. y);} int ret = mo_graham (n, dian, zhan); double area = mo_area_polygon (zhan, ret); printf ("%. 0lf \ n ", floor (area/50);} return 0 ;}