改革春风吹满地

 1 #include <stdio.h> 
 2  
 3 double get_area(double a,double b,double c,double d,double e,double f); 
 4 
 5 int main(){
 6     int n;
 7     double x[101];
 8     double y[101];
 9     int i;
10     double total_area;
11     
12     while(1){
13         scanf("%d",&n);
14         
15         if(n==0)
16             break;
17         
18         total_area=0;    
19         for(i=0;i<n;i++)
20             scanf("%lf%lf",&x[i],&y[i]);
21             
22         for(i=0;i<n-2;i++){  //默认0,0为多边形顶点,求n-2个三角形的面积和 
23             total_area+=get_area(x[0],y[0],x[i+1],y[i+1],x[i+2],y[i+2]);
24         }
25         
26         printf("%.1lf\n",total_area);
27     }
28     
29     return 0;
30 }
31 
32 double get_area(double a,double b,double c,double d,double e,double f){  //已知三点坐标求面积 
33     double area;
34     
35     area=(a*d+b*e+c*f-a*f-b*c-d*e)/2;   //不用加绝对值 
36     
37     return area;
38 }