c语言 输入三角形的三条边或者三个顶点的坐标求三角形面积
#include <iostream>
#include<>
#include<>
#include<queue>
#include<algorithm>
#include<string>
#include<>
#include<map>
#include<set>
#include <sstream>
using namespace std;
typedef long long ll;
const ll maxn=1e2+10;
const ll mod= 1000000007;
int main()
{
double x1,y1,x2,y2,x3,y3;
cin >>x1 >>y1 >>x2>>y2>>x3>>y3;
double a,b,c;
a=sqrt((y2-y1)*(y2-y1)+(x2-x1)*(x2-x1));
b=sqrt((y3-y1)*(y3-y1)+(x3-x1)*(x3-x1));
c=sqrt((y2-y3)*(y2-y3)+(x2-x3)*(x2-x3));
double s;
s=(a+b+c)/2;//计算半周长
double area;
area= sqrt(s*(s-a)*(s-b)*(s-c));//套用海伦公式，计算面积
cout << area <<endl;
}