//我的最简洁
#include <bits/stdc++.h>
using namespace std;
int main(){
	double x1,x2,x3,y1,y2,y3,a,b,c,t;
	cin>>x1>>y1>>x2>>y2>>x3>>y3;
	a=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)); 
	b=sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3)); 
	c=sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3)); 
	t=(a+b+c)/2;
	cout << fixed << setprecision(2)<<sqrt(t*(t-a)*(t-b)*(t-c));
	return 0;
}

#include <bits/stdc++.h>
using namespace std;
int main(){
	double x1,x2,x3,y1,y2,y3,a,b,c,t;
	cin>>x1>>y1>>x2>>y2>>x3>>y3;
	a=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)); 
	b=sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3)); 
	c=sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3)); 
	t=(a+b+c)/2;
	cout << fixed << setprecision(2)<<sqrt(t*(t-a)*(t-b)*(t-c));
	return 0;
}

#include <bits/stdc++.h>
using namespace std;
int main(){
	double x1,x2,x3,y1,y2,y3,a,b,c,t;
	cin>>x1>>y1>>x2>>y2>>x3>>y3;
	a=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)); 
	b=sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3)); 
	c=sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3)); 
	t=(a+b+c)/2;
	cout << fixed << setprecision(2)<<sqrt(t*(t-a)*(t-b)*(t-c));
	return 0;
}

水题！

#include <bits/stdc++.h>
using namespace std;
double x1,x2,y1,y2,x3,y3,t;
int main(){
	cin>>xa>>ya>>xb>>yb;
	double an=sqrt(x1*x1+y1*y1);
     double ban=sqrt(x2*x2+y2*y2);
     double can=sqrt(x3*x3+y3*y3);
     double t=(an+ban+can)*1.0/2  
     	cout<<fixed<<setprecision(2)<<t<<endl;
	return 0；

#include <bits/stdc++.h>
using namespace std;
int main(int argc, char **argv){
	double x1,x2,x3,y1,y2,y3,r,x,y,z;
	cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
	x = sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)); 
	y = sqrt((x1 - x3) * (x1 - x3) + (y1 - y3) * (y1 - y3)); 
	z = sqrt((x2 - x3) * (x2 - x3) + (y2 - y3) * (y2 - y3)); 
	r = (x + y + z) / 2;
	printf("%.2f",sqrt(r * (r - x) * (r - y) * (r - z)));
	return 0;
}

#include <set>
#include <ios>
#include <list>
#include <cmath>
#include <ctime>
#include <queue>
#include <deque>
#include <stack>
#include <vector>
#include <bitset>
#include <cctype>
#include <cerrno>
#include <cwchar>
#include <cstdio>
#include <fenv.h>
#include <iosfwd>
#include <string>
#include <limits>
#include <math.h>
#include <cstdlib>
#include <iomanip>
#include <clocale>
#include <complex>
#include <cstring>
#include <cstring>
#include <cwctype>
#include <istream>
#include <ostream>
#include <sstream>
#include <fstream>
#include <utility>
#include <stdio.h>
#include <iostream>
#include <stdint.h>
#include <string.h>
#include <tgmath.h>
#include <complex.h>
#include <algorithm>
#include <exception>
#include <stdbool.h>
#include <stdexcept>
#include <streambuf>
#include <functional>
#include <inttypes.h>
#include <bits/stdc++.h>
using namespace std;
int main(){
	double x1,x2,x3,y1,y2,y3,a,b,c,t;
	cin>>x1>>y1>>x2>>y2>>x3>>y3;
	a=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)); 
	b=sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3)); 
	c=sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3)); 
	t=(a+b+c)/2;
	cout << fixed << setprecision(2)<<sqrt(t*(t-a)*(t-b)*(t-c));
	return 0;
}

#include<bits/stdc++.h> using namespace std; int main(){ double x1,x2,y1,y2,x3,y3; double ch1=0,ku1=0,ch2=0,ku2=0; double smj=0,djs1=0,djs2=0,djs3=0; double ch3=0,ku3=0,bzc=0; double pj1=0,pj2=0,pj3=0; scanf("%lf%lf",&x1,&y1); scanf("%lf%lf",&x3,&y3); scanf("%lf%lf",&x2,&y2); ch1=y3-y2; ch2=y3-y1; ch3=y2-y1; ku1=x2-x1; ku2=x3-x2; ku3=x3-x1; if(ch1<0){ ch1=0-ch1; } if(ku1<0){ ku1=0-ku1; } if(ch2<0){ ch2=0-ch2; } if(ch3<0){ ch3=0-ch3; } if(ku2<0){ ku2=0-ku2; } if(ku3<0){ ku3=0-ku3; } djs1=sqrt(ch1ch1+ku1ku1); djs2=sqrt(ch2ch2+ku2ku2); djs3=sqrt(ch3ch3+ku3ku3); bzc=(djs1+djs2+djs3)/2; pj1=bzc-djs1; pj2=bzc-djs2; pj3=bzc-djs3; smj=sqrt(bzcpj1pj2*pj3); cout<<fixed<<setprecision(2)<<smj; return 0; } 哪位大佬能看出那里错了

#include <bits/stdc++.h> using namespace std;

int main(){ double x1,x2,x3,y1,y2,y3,t; cin>>x1>>y1>>x2>>y2>>x3>>y3; double an=sqrt((x1-x2)(x1-x2)+(y1-y2)(y1-y2)); double ban=sqrt((x2-x3)(x2-x3)+(y2-y3)(y2-y3)); double can=sqrt((x3-x1)(x3-x1)+(y1-y3)(y1-y3)); t=(an+ban+can)1.0/2 ;吵 cout<<fixed<<setprecision(2)<<sqrt(t(t-an)(t-ban)(t-can))<<endl;查查查 return 0; }

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main() {
    double xa,ya,xb,yb,xc,yc,a,b,c,d,e,f,g,h,i,j,t,k,l,m;
    cin>>xa>>ya>>xb>>yb>>xc>>yc;
    a=xb-xa;
    b=yb-ya;
    c=sqrt(a*a+b*b);//勾股定理求a
    d=xc-xb;
    e=yc-yb;
    f=sqrt(d*d+e*e);//勾股定理求b
    g=xc-xa;
    h=yc-ya;
    i=sqrt(g*g+h*h);//勾股定理求c
    j=c+f+i;
    t=j/2;
    k=t-c;
    l=t-f;
    m=t-i;
    cout << fixed << setprecision(2)<<sqrt(t*k*l*m);//海伦公式求面积
    return 0;
}