# include "stdio.h"
# include "math.h"
float length(int a,int b,int c,int d);
int main(void)
{
	int a[3][2],i;
	float perimeter=0,l1,l2,l3;
	for(i=0;i<3;i++)//输入三边坐标 
	{
		scanf("%d%d",&a[i][0],&a[i][1]);
	}
	l1=length(a[0][0],a[0][1],a[1][0],a[1][1]);
	l2=length(a[1][0],a[1][1],a[2][0],a[2][1]);
	l3=length(a[0][0],a[0][1],a[2][0],a[2][1]);
	perimeter=l1+l2+l3;
	printf("%.2f",perimeter);
} 
float length(int a,int b,int c,int d)
{
	float z;
	z=sqrt((a-c)*(a-c)+(b-d)*(b-d));
	return (z);
}

第五个错了，求教