C语言编程题 题目：任意输入4个点，求围成四边形的面积

//
// 算法说明：
// 凸四边形任意一条边的两个顶点位于另外两个顶点所在直线的同一侧
// 凹四边形有两条边的两个顶点位于另外两个顶点所在直线的两侧
// 四个点（0,1,2,3）围成4边形可能的顺序有3种情况：0123 0213 0132
//
#include
#include
#define ESP (1e-6)
double x[4]={0.0},y[4]={0.0};
double A[6],B[6],C[6];//直线方程 Ax+By+C=0
double D[6],E[6];//D、E保存另外两点带入直线方程的值，为零表示点在直线上，符号相同表示位于直线的同一侧
int pos[6][4]={{0,1,2,3},{0,2,1,3},{0,3,1,2},{1,2,0,3},{1,3,0,2},{2,3,0,1}};//用于数组ABCDEF
char str[6][8]={"0,1,2,3","0,2,1,3","0,3,1,2","1,2,0,3","1,3,0,2","2,3,0,1"};//用于打印输出
void TriangleArea(int a,int b, int c, int d)
{
double S;
if(((x[a]-x[b])*(x[a]-x[c])<0) || ((y[a]-y[b])*(y[a]-y[c])<0))
{
S = fabs(x[b]*y[c]-y[b]*x[c]+x[c]*y[d]-x[d]*y[c]+x[d]*y[b]-x[b]*y[d]);
printf("三点(%5.2lf,%5.2lf)(%5.2lf,%5.2lf)(%5.2lf,%5.2lf)共线，三角形(%5.2lf,%5.2lf)(%5.2lf,%5.2lf)(%5.2lf,%5.2lf)\n面积S=%lf\n",
x[a],y[a],x[b],y[b],x[c],y[c],x[b],y[b],x[c],y[c],x[d],y[d],S);
}
else if(((x[b]-x[a])*(x[b]-x[c])<0) || ((y[b]-y[a])*(y[b]-y[c])<0))
{
S = fabs(x[a]*y[c]-y[a]*x[c]+x[c]*y[d]-x[d]*y[c]+x[d]*y[a]-x[a]*y[d]);
printf("三点(%5.2lf,%5.2lf)(%5.2lf,%5.2lf)(%5.2lf,%5.2lf)共线，三角形(%5.2lf,%5.2lf)(%5.2lf,%5.2lf)(%5.2lf,%5.2lf)\n面积S=%lf\n",
x[a],y[a],x[b],y[b],x[c],y[c],x[a],y[a],x[c],y[c],x[d],y[d],S);
}
else if(((x[c]-x[a])*(x[c]-x[b])<0) || ((y[c]-y[a])*(y[c]-y[b])<0))
{
S = fabs(x[a]*y[c]-y[a]*x[c]+x[c]*y[d]-x[d]*y[c]+x[d]*y[a]-x[a]*y[d]);
printf("三点(%5.2lf,%5.2lf)(%5.2lf,%5.2lf)(%5.2lf,%5.2lf)共线，三角形(%5.2lf,%5.2lf)(%5.2lf,%5.2lf)(%5.2lf,%5.2lf)\n面积S=%lf\n",
x[a],y[a],x[b],y[b],x[c],y[c],x[a],y[a],x[b],y[b],x[d],y[d],S);
}
}
//凹四边形
void AoArea01122330()
{
double S = fabs(x[0]*y[1]-x[1]*y[0]+x[1]*y[2]-x[2]*y[1]+x[2]*y[3]-x[3]*y[2]+x[3]*y[0]-x[0]*y[3])/2;
printf("凹四边形\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\n面积S=%lf\n",
x[0],y[0],x[1],y[1],x[2],y[2],x[3],y[3],S);
}
void AoArea01133220()
{
double S = fabs(x[0]*y[1]-x[1]*y[0]+x[1]*y[3]-x[3]*y[1]+x[3]*y[2]-x[2]*y[3]+x[2]*y[0]-x[0]*y[2])/2;
printf("凹四边形\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\n面积S=%lf\n",
x[0],y[0],x[1],y[1],x[3],y[3],x[2],y[2],S);
}
void AoArea02211330()
{
double S = fabs(x[0]*y[2]-x[2]*y[0]+x[2]*y[1]-x[1]*y[2]+x[1]*y[3]-x[3]*y[1]+x[3]*y[0]-x[0]*y[3])/2;
printf("凹四边形\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\n面积S=%lf\n",
x[0],y[0],x[2],y[2],x[1],y[1],x[3],y[3],S);
}
//凸四边形
void Area01122330()
{
double S = fabs(x[0]*y[1]-x[1]*y[0]+x[1]*y[2]-x[2]*y[1]+x[2]*y[3]-x[3]*y[2]+x[3]*y[0]-x[0]*y[3])/2;
printf("凸四边形\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\n面积S=%lf\n",
x[0],y[0],x[1],y[1],x[2],y[2],x[3],y[3],S);
}
void Area01133220()
{
double S = fabs(x[0]*y[1]-x[1]*y[0]+x[1]*y[3]-x[3]*y[1]+x[3]*y[2]-x[2]*y[3]+x[2]*y[0]-x[0]*y[2])/2;
printf("凸四边形\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\n面积S=%lf\n",
x[0],y[0],x[1],y[1],x[3],y[3],x[2],y[2],S);
}
void Area02211330()
{
double S = fabs(x[0]*y[2]-x[2]*y[0]+x[2]*y[1]-x[1]*y[2]+x[1]*y[3]-x[3]*y[1]+x[3]*y[0]-x[0]*y[3])/2;
printf("凸四边形\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\t(%5.2lf,%5.2lf)\n面积S=%lf\n",
x[0],y[0],x[2],y[2],x[1],y[1],x[3],y[3],S);
}
int CheckInput()
{
//判断输入的4个点是不同的四个点
if((fabs(x[0]-x[1])(fabs(x[0]-x[2])(fabs(x[0]-x[3])(fabs(x[1]-x[2])(fabs(x[1]-x[3])(fabs(x[2]-x[3])return 0;
return 1;
}
//判断是否是凸四边形 0123
int Check01122330(double *D, double *E)
{
if(D[0]*E[0]>0 && D[2]*E[2]>0 && D[3]*E[3]>0 && D[5]*E[5]>0)
return 1;
else
return 0;
}
//判断是否是凸四边形 0132
int Check01133220(double *D, double *E)
{
if(D[0]*E[0]>0 && D[1]*E[1]>0 && D[4]*E[4]>0 && D[5]*E[5]>0)
return 1;
else
return 0;
}
//判断是否是凸四边形 0213
int Check02211330(double *D, double *E)
{
if(D[1]*E[1]>0 && D[2]*E[2]>0 && D[3]*E[3]>0 && D[4]*E[4]>0)
return 1;
else
return 0;
}
void Calculate(int p, double *A, double *B, double *C, double *D, double *E)
{
int p1=pos[p][0];
int p2=pos[p][1];
int p3=pos[p][2];
int p4=pos[p][3];
if(fabs(y[p2]-y[p1]){
*A = 0.0;
*B = 1.0;
*C = -y[p1];
}
else if(fabs(x[p2]-x[p1]){
*A = 1.0;
*B = 0.0;
*C = -x[p1];
}
else
{
double t=(x[p2]-x[p1])/(y[p2]-y[p1]);
*A = 1.0;
*B = -t;
*C = t*y[p1]-x[p1];
}
*D = *A * x[p3] + *B * y[p3] + *C;
*E = *A * x[p4] + *B * y[p4] + *C;
}
int main()
{
double t;
int i,ii;
do
{
for(i=0;i<4;i++)
{
printf("Please Input Point %d(x,y):", i+1);
scanf("%lf,%lf", &x[i],&y[i]);
}
}while(CheckInput()==0);//检查输入的是4个不同的点
for(i=0;i<6;i++)
{
Calculate(i,&A[i],&B[i],&C[i],&D[i],&E[i]);
printf("(%s)\tA=%5.2lf\tB=%5.2lf\tC=%5.2lf\tD=%5.2lf\tE=%5.2lf\n", str[i], A[i], B[i], C[i], D[i], E[i]);
}
//判断4点共线
if(fabs(D[0]){
printf("四点共线，面积为零\n");
return 0;
}
//判断3点共线
if(fabs(D[0]){
//0,1,2三点共线
TriangleArea(0,1,2,3);
return 0;
}
else if(fabs(E[0]){
//0,1,3三点共线
TriangleArea(0,1,3,2);
return 0;
}
else if(fabs(E[1]){
//0,2,3三点共线
TriangleArea(0,2,3,1);
return 0;
}
else if(fabs(E[3]){
//1,2,3三点共线
TriangleArea(1,2,3,0);
return 0;
}
//四边形
if(Check01122330(D,E)==0 && Check01133220(D,E)==0 && Check02211330(D,E)==0)
{
//凹四边形
AoArea01122330();
AoArea01133220();
AoArea02211330();
}
else if(Check01122330(D,E)==1)
{
//凸四边形
Area01122330();
}
else if(Check01133220(D,E)==1)
{
//凸四边形
Area01133220();
}
else if(Check02211330(D,E)==1)
{
//凸四边形
Area02211330();
}
return 0;
}