计算距离检测地点最近的点，距离相同的点序号小的最近

 代码如下：

#include <stdio.h>
#include <math.h>
//距离计算
double D(double a,double b,double m,double n) 
{
	double D;
	double Dx2 = pow((a-m),2.0);
	double Dy2 = pow((b-n),2.0);
	D = sqrt (Dx2 + Dy2);
	return (D);
}
int main()
{
	int n,x,y;
	//a[i][0]为X，a[i][1]为Y，a[i][2]为该检测点与市民的距离，a[i][3]为检测点的编号
	double a[201][4];
	double t;
	int i,j;
	scanf("%d %d %d",&n,&x,&y);
	for(i=0;i<n;i++)
	{
		scanf("%lf %lf",&a[i][0],&a[i][1]);
		a[i][2] = D(a[i][0], a[i][1], x, y);//两点之间的距离
		a[i][3] = i+1;//监测点的编号	
	}
	//将距离和相应的检测点编号进行冒泡排列
	for(i = 0; i < n; i++)
	{
		for (j = 0; j < n - i -1; j++)
		{
			if (a[j][2] > a[j+1][2])
			{
				t = a[j][2];
				a[j][2] = a[j+1][2];
				a[j+1][2] = t;
				
				t = a[j][3];
				a[j][3] = a[j+1][3];
				a[j+1][3] = t;
			}
		}
	} 
	//输出前三的序号 
	for (i = 0; i < 3; i++)
	{
		printf("%d\n", (int)a[i][3]);
	}
	return 0; 
}