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 <cstdio>
using namespace std;

signed main() {
  int n;

  cin >> n;
  while (n--) {
    double x[4], y[4];
    for (int i = 0; i < 4; cin >> x[i] >> y[i], i++);
    double vx1 = x[1] - x[0], vy1 = y[1] - y[0],
           vx2 = x[3] - x[2], vy2 = y[3] - y[2];
    if (vx1 * vy2 - vy1 * vx2 == 0) {
      puts("YES");
    } else {
      puts("NO");
    }
  }

  return 0;
}

C++: #include<iostream>
#include<cmath>
using namespace std;
int main()
{
	int n;cin>>n;
	for(;n--;)
	{
		double a,b,c,d,e,f,g,h;cin>>a>>b>>c>>d>>e>>f>>g>>h;
		if(abs(c-a)<1e-8||abs(g-e)<1e-8)cout<<(abs(c-a)<1e-8&&abs(g-e)<1e-8?"YES":"NO")<<endl;
		else cout<<(abs((d-b)*(g-e)-(h-f)*(c-a))<1e-8?"YES":"NO")<<endl;
	}
}

C++: #include <bits/stdc++.h>

#define REP(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rep(i, n) REP (i, 0, n)
#define mset(a, n) memset(a, n, sizeof(a))

using namespace std;

int main() {
	int n; cin >> n;
	while (n--) {
		double x1, y1, x2, y2, x3, y3, x4, y4;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		// 対角線の中点で判定
		// double cx1 = (x3 - x1) / 2.0;
		// double cy1 = (y3 - y1) / 2.0;
		// double cx2 = (x4 - x2) / 2.0;
		// double cy2 = (y4 - y2) / 2.0;
		// if (cx1 == cx2 && cy1 == cy2) {
		//  cout << "YES" << endl;
		// } else {
		//  cout << "NO" << endl;
		// }
		// 傾きで判定
		if (x1 == x2 && x3 == x4) {
			cout << "YES" << endl;
		} else if (x1 == x2 || x3 == x4) {
			cout << "NO" << endl;
		} else if ((y2 - y1) / (x2 - x1) == (y4 - y3) / (x4 - x3)) {
			cout << "YES" << endl;
		} else {
			cout << "NO" << endl;
		}
	}
}

C++: #include<stdio.h>

int main()
{
	int n;
	double x1,y1,x2,y2,x3,y3,x4,y4,p,q;

	scanf("%d",&n);
	for(int x=0;x<n;x++)
	{
		for(;;)
		{
			scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);
			if(x1>=100||y1>=100||x2>=100||y2>=100||x3>=100||y3>=100||x4>=100||y4>=100)
			{
			}
			if(x1<=-100||y1<=-100||x2<=-100||y2<=-100||x3<=-100||y3<=-100||x4<=-100||y4<=-100)
			{
			}
			else
			{
				break;
			}
		}

		x2-=x1;
		y2-=y1;
		x1=0;
		y1=0;
		x4-=x3;
		y4-=y3;
		x3=0;
		y3=0;

		p=x2/x4;
		q=y2/y4;

		if(p==q)
		{
			printf("YES\n");
		}
		else
		{
			printf("NO\n");
		}
	}
	return 0;
}

C++: #include<iostream>

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

C++: #include <vector>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <algorithm>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <string>
#include <cstring>
#include <complex>
#include <ctime>
#include <cstdlib>

using namespace std;

inline int to_int(string s) {int v; istringstream sin(s); sin >> v; return v;}
template<class T> inline string to_str(T x) {ostringstream sout; sout << x; return sout.str();}

typedef long long ll;

int main()
{
	int num;
	double sx1, sy1, sx2, sy2;
	double ex1, ey1, ex2, ey2;

	cin >> num;

	for(int i = 0; i < num; i++)
	{
		cin >> sx1 >> sy1 >> sx2 >> sy2 >> ex1 >> ey1 >> ex2 >> ey2;

		if( (sy2-sy1)/(sx2 - sx1) == (ey2-ey1)/(ex2-ex1))
		{
			cout << "YES" << endl;
		}
		else
		{
			cout << "NO" << endl;
		}
	}
}

C++: #include <iostream>

using namespace std;

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

C++: #include<iostream>
using namespace std;
int main() {
	double zhyoxy[4], line1, line2;
	char hantei[2];
	int time;
	cin >> time;
	for (int i = 0; i < time; ++i) {
		for (int i = 0; i < 4; ++i) {
			cin >> zhyoxy[i];
		}
		if (zhyoxy[3] == zhyoxy[1]) {
			hantei[0] = 'y';
		}
		else if (zhyoxy[2] == zhyoxy[0]) {
			hantei[0] = 'x';
		}
		line1 = (zhyoxy[3] - zhyoxy[1]) / (zhyoxy[2] - zhyoxy[0]);
		for (int i = 0; i < 4; ++i) {
			cin >> zhyoxy[i];
		}
		if (zhyoxy[3] == zhyoxy[1]) {
			hantei[1] = 'y';
		}
		else if (zhyoxy[2] == zhyoxy[0]) {
			hantei[1] = 'x';
		}
		line2 = (zhyoxy[3] - zhyoxy[1]) / (zhyoxy[2] - zhyoxy[0]);
		if (line1 == line2||zhyoxy[0]==zhyoxy[1]) {
			cout << "YES" << endl;
		}
		else {
			cout << "NO" << endl;
		}
	}
	return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <stdio.h>

using namespace std;

int n;
double x1, x2, x3, x4, y1, y2, y3, y4, slope1, slope2;

double abs(double s) {
    return s < 0 ? -s : s;
}

int main(void) {
    cin >> n;
    while(n--) {
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
        slope1 = (y1 - y2) / (x1 - x2);
        slope2 = (y3 - y4) / (x3 - x4);

        if(slope1 == slope2) {
            cout << "YES" << endl;
        } else {
            cout << "NO" << endl;
        }
    }
    return 0;
}

C++: //0021
#include <bits/stdc++.h>
using namespace std;

int main(){
	double x1,y1,x2,y2,x3,y3,x4,y4;
	double AB,CD;
	int n;
	cin>>n;
	while(n--){
		cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;

		AB = (y1-y2)/(x1-x2);
		CD = (y3-y4)/(x3-x4);
		if(AB == CD)
			cout<<"YES"<<endl;

		else
			cout<<"NO"<<endl;
	}
	return 0;
}
//0021
#include <bits/stdc++.h>
using namespace std;

int main(){
	double x1,y1,x2,y2,x3,y3,x4,y4;
	double AB,CD;
	int n;
	cin>>n;
	while(n--){
		cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;

		AB = (y1-y2)/(x1-x2);
		CD = (y3-y4)/(x3-x4);
		if(AB == CD)
			cout<<"YES"<<endl;

		else
			cout<<"NO"<<endl;
	}
	return 0;
}

C++: #include <cstdio>
#include <cmath>
#include <cfloat>

int n;

int main(){
	scanf("%d", &n);
	for(int i = 0; i < n; ++i){
		double x[4][2];
		for(int j = 0; j < 4; ++j){
			scanf("%lf%lf", x[j], x[j] + 1);
		}
		double y[2][2] = {
			{x[0][0] - x[1][0], x[0][1] - x[1][1]},
			{x[2][0] - x[3][0], x[2][1] - x[3][1]}
		};

		//printf("%lf\n", y[0][0] * y[1][1] - y[0][1] * y[1][0]);

		if(std::abs(y[0][0] * y[1][1] - y[0][1] * y[1][0]) < 1e-9){
			printf("YES\n");
		}
		else{
			printf("NO\n");
		}
	}
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
int main(){
  double n,x1,x2,x3,x4,y1,y2,y3,y4;
  cin >> n;
  for(int i=0;i<n;i++){
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
    if(abs(y1-y2)/abs(x1-x2)==abs(y3-y4)/abs(x3-x4)){
      cout << "YES" << endl;
    }else{
      cout << "NO" << endl;
    }
  }
  return 0;
}

C++: #include<iostream>
#include<cmath>
#include<cassert>
#include<cstdlib>
using namespace std;
#define EPS 0.0000001


main(){
	int tcase;   cin >> tcase;
	double x1, y1, x2, y2, x3, y3, x4, y4;
	for (int i = 0; i < tcase; i++){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;


		if (abs((y2 - y1)*(x4 - x3) - (y4 - y3)*(x2 - x1)) < EPS) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
}