#include <stdio.h>
#include <stdlib.h>
#include <math.h>
main()
{
float a,b,c,s,area;
printf("please enter nums: ");
scanf("%f%f%f",&a,&b,&c);
if((a+b > c) && (a+c > b) && (c+b > a))
{
s = 1.0/2*(a + b + c);
area = sqrt(s *(s - a)*(s - b)*(s - c));
printf("the area is %f\n",area);
}
else
printf("不是三角形");
}