Go: package main

import (
        "fmt"
        "math/big"
)

func main() {
        var x1, x2, x3, x4, y1, y2, y3, y4 big.Float
        var n int
        fmt.Scanf("%d", &n)
        for i := 0; i < n; i++ {
                fmt.Scanf("%f %f %f %f %f %f %f %f",
                        &x1, &y1, &x2, &y2, &x3, &y3, &x4, &y4)
                var lx, ly, mx, my, mul1, mul2, sub, zz big.Float
                lx.Sub(&x2, &x1)
                ly.Sub(&y2, &y1)
                mx.Sub(&x4, &x3)
                my.Sub(&y4, &y3)
                mul1.Mul(&lx, &my)
                mul2.Mul(&ly, &mx)
                sub.Sub(&mul1, &mul2)
                zz.SetFloat64(0.0)

                if sub.Cmp(&zz) == 0 {
                        fmt.Println("YES")
                } else {
                        fmt.Println("NO")
                }
        }
}

C++: #include<iostream>
#include<cmath>
using namespace std;
int main(){
  int n; cin >> n;
  while(n--){
    double x[4],y[4];
    for(int i=0;i<4;i++) cin >> x[i] >> y[i]; 
    if(abs((x[3] - x[2]) * (y[1] - y[0]) - (x[1] - x[0]) * (y[3] - y[2])) < 1e-10)
      cout<<"YES"<<endl;
    else
      cout<<"NO"<<endl;
  }
}

C++: #include <iostream>
using namespace std;

int main(void){
    int n;
    double x[4];
    double y[4];
    cin >> n;
    while(n--){
        for(int i=0;i<4;i++) cin >> x[i] >> y[i];
        double ll,lll;
        ll = (y[1]-y[0])/(x[1]-x[0]);
        lll = (y[3]-y[2])/(x[3]-x[2]);
        if(ll == lll) cout << "YES" << endl;
        else cout << "NO" << endl;
    }
    return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <string>
#include <cmath>
#include <stack>
using namespace std;

int main(){
	int n;
	cin >> n;
	double x1,y1,x2,y2,x3,y3,x4,y4;
	while(cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4){
		if((y1 - y2)/(x1 - x2) == (x3 - x4)/(y3 - y4))cout << "YES" << endl;
		else cout << "NO" << endl;
	}
}

C++: #include<iostream>
using namespace std;

struct Pos {
	double x, y;
}a, b, c, d;

int main() {
	int n;
	cin >> n;
	for(int i = 0; i < n; i++ ) {
		cin >> a.x >> a.y >> b.x >> b.y >> c.x >> c.y >> d.x >> d.y;
		Pos e;
		e.x = b.x - a.x;
		e.y = b.y - a.y;
		Pos f;
		f.x = d.x - c.x;
		f.y = d.y - c.y;
		
		double men = e.x * f.y - e.y * f.x;
		double eps = 1e-9;
		if(-eps <= men && men <= eps)
			cout << "YES" << endl;
		else
			cout << "NO" << endl;
	}
	return 0;
}

C++: #include <iostream>
using namespace std;
double x1,y1,x2,y2;
double a,b,c,d;

double chaji(){
	double dx=x2-x1,dy=y2-y1;
	double aa=c-a,bb=d-b;
	return (dx*bb-dy*aa);
}
int main(){
	int N;cin>>N;
	while(N--){
		cin>>a>>b>>c>>d;
		cin>>x1>>y1>>x2>>y2;
		double ans1=chaji();
		x1=(x1+x2)/2;
		y1=(y1+y2)/2;
		x2=(a+c)/2;
		y2=(b+d)/2;
		double ans2=chaji();
		if(ans1==0&&ans2!=0)cout<<"YES"<<endl;
		else cout<<"NO"<<endl;
	}
}

C++: #include <iostream>
using namespace std;
typedef struct vec vec;

struct vec {
	double x, y;
};

static vec P(double x, double y){
	vec P = {x, y};
	return P;
}

static vec sub(vec a, vec b){
	return P(a.x - b.x, a.y - b.y);
}

static double cross(vec a, vec b){
	return (a.x * b.y - a.y * b.x);
}

int main(void){
    
int n;
cin >> n;
double D[8];
vec V[4];
for(int i = 0; i < n; i++){
	for(int j = 0; j < 4; j++){
		cin >> D[2*j] >> D[2*j+1];
		V[j] = P(D[2*j], D[2*j+1]);
	}
	vec a = sub(V[0], V[1]);
	vec b = sub(V[2], V[3]);
	if (cross(a, b) == 0)
		cout << "YES" << endl;
	else
		cout << "NO" << endl;
}
return 0;

}

C++: #include <iostream>
#include <algorithm>
#include <cctype>
#include <cstdio>
#include <math.h>
using namespace std;

int main() {
	
	int n;
	double x1,y1,x2,y2,x3,y3,x4,y4,m1,m2;
	
	cin>>n;
	
	for(int i=0;i<n;i++){
		int p=0;
		cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
		if(x1==x2&&x3==x4){p=1;}
		else if(x1==x2||x3==x4){}
		else if((y2-y1)/(x2-x1)==(y4-y3)/(x4-x3))p=1;
		if(p==1)cout<<"YES"<<endl;
		else cout<<"NO"<<endl;
	}
	
	return 0;
}

C++: #include<iostream>
using namespace std;
#define rep(i,a) for(int i = 0 ; i < a ;  i++)
int main(void){
	int n;
	cin>>n;
	rep(k,n){
		double x[4];
		double y[4];
		double ans[2];
		rep(i,4)cin>>x[i]>>y[i];
    ans[0]=(y[1]-y[0])/(x[1]-x[0]);
    ans[1]=(y[3]-y[2])/(x[3]-x[2]);
		if(ans[0]==ans[1])cout<<"YES";
		else cout<<"NO";
		cout<<endl;
	}
}

C++: #include<cmath>
#include<algorithm>
#include<iostream>
#include<vector>
#include<climits>
#include<cfloat>
 
using namespace std;
 
double EPS = 1e-10;
const double PI = acos(-1);
 
double add(double a, double b){
  if(abs(a+b) < EPS * (abs(a)+abs(b)))return 0;
  return a+b;
}
 
struct point{
  double x, y;
  point(){x=y=0;}
  point(double x,double y) : x(x) , y(y){}
 
  point operator - (point p){
    return point(add(x,-p.x), add(y,-p.y));
  }
};
 
double cross(point a, point b) {return (a.x * b.y - a.y * b.x);}
 
int is_parallel(point a1, point a2, point b1, point b2) {
  return cross(a1-a2, b1-b2)==0.0 ;
}
 
int main(void){
 
  point a,b,c,d;
  int n;
  cin >> n;
 
  while(n--){
    cin >> a.x >> a.y >> b.x >> b.y;
    cin >> c.x >> c.y >> d.x >> d.y;
    if(is_parallel(a,b,c,d))cout << "YES" << endl;
    else cout << "NO" << endl;
  }
 
  return 0;
}

C++: #include <complex>
#include <iostream>
#include <cmath>
using namespace std;

typedef complex<double> xy_t;
double cross_product(xy_t a, xy_t b) { return (conj(a)*b).imag(); }
const double eps = 1e-11;
double x[4],y[4];
int N;
int main() {
	cin >> N;
	for (int i=0; i<N; ++i) {
		for (int i=0; i<4; ++i) {
			cin >> x[i] >> y[i];
		}
		xy_t a[2] = {
					xy_t(x[0],y[0]) - xy_t(x[1],y[1]),
					xy_t(x[2],y[2]) - xy_t(x[3],y[3])
				};
		bool p = abs(cross_product(a[0],a[1]))/2 < eps;
		cout << ( p ? "YES" : "NO") << endl;
	}
}