计算三角形面积

#include<stdio.h>

#include<math.h> //主要是用pow函数

double changdu(double x1,double x2,double y1,double y2)

{

    double changdu = 0;

    changdu = pow(pow(x1-x2,2) + pow(y1-y2,2),0.5);

    return changdu;

}

int main()

{

    double xa1,xa2,xa3,ya1,ya2,ya3,a,b,c,p,s;

    scanf("%lf%lf",&xa1,&ya1);

    scanf("%lf%lf",&xa2,&ya2);

    scanf("%lf%lf",&xa3,&ya3);

    a = changdu(xa1,xa2,ya1,ya2);

    b = changdu(xa1,xa3,ya1,ya3);

    c = changdu(xa2,xa3,ya2,ya3);

    p =  (a + b + c)/2;

    s =  pow(p*(p-a)*(p-b)*(p-c),0.5);//海伦公式

    printf("%.2f\n",s);

    return 0 ;

}