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<stdio.h>
#include<math.h>

int main(){
	double x1,x2,x3,x4,y1,y2,y3,y4;
	double yoko1,yoko2,tate1,tate2;
	int ans[100]={0};
	int n,i;
	
	scanf("%d",&n);
	
	for(i=0;i<n;i++){
	scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&x1,&x2,&x3,&x4,&y1,&y2,&y3,&y4);
	yoko1=(x1-x3)*(x1-x3);
	yoko2=(x2-x4)*(x2-x4);
	tate1=(y1-y3)*(y1-y3);
	tate2=(y2-y4)*(y2-y4);
	
	if(sqrt(yoko1+tate1)==sqrt(yoko2+tate2))ans[i]=1;
	else ans[i]=0;
	}
	
	for(i=0;i<n;i++){
		if(ans[i]==1)printf("YES\n");
		else printf("NO\n");
	}
return 0;
}

C++: #include <stdio.h>

int main(){
	int num;
	double x1, y1;
	double x2, y2;
	double x3, y3;
	double x4, y4;
	long long ax, ay;
	long long bx, by;
	long long s;
			
	scanf("%d", &num);	
	for(int i = 0; i < num; i++){
		scanf("%lf %lf %lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3, &x4, &y4);
		
		ax = x2 - x1;
		ay = y2 - y1;
		bx = x4 - x3;
		by = y4 - y3;
		s = ax*by - ay*bx;
		if(s == 0){
			printf("YES\n");
		}else{
			printf("NO\n");
		}
	}
	
	return 0;
}

C++: #include<stdio.h>
 
int main(void){
    double x[4],y[4];
    int n,i;
     
    scanf("%d",&n);
     
    for(i=0;i<n;i++){
        scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&x[0],&y[0],&x[1],&y[1],&x[2],&y[2],&x[3],&y[3]);
         
        if(((y[1]-y[0])/(x[1]-x[0])) == ((y[3]-y[2])/(x[3]-x[2])))printf("YES\n");
        else printf("NO\n");
    }
     
    return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <vector>
#include <list>
#include <algorithm>
#include <cmath>
#include <stack>
#include <set>
using namespace std;

#define REP(i,n) for(int (i)=0; (i)<(n); (i)++)
#define FOR(i,a,b) for(int (i)=(a); (i)<(b); (i)++)
#define PUSH(n,v) for(int i=0; i<(n); i++) {int j; cin >> j; v.push_back(j);}
#define ALL(v) v.begin(), v.end()

typedef pair<double, double> XY;

bool para(XY p, XY q) {
    double k;
    if (p.first == 0 && q.first == 0) return true;
    if (p.first == 0 || q.first == 0) return false;
    else k = q.first / p.first;
    if ((abs(p.second * k - q.second) * 1000000000000) < 1) return true;
    return false;
}

int main() {
    int n;
    cin >> n;
    REP(i,n) {
        double ax, ay, bx, by, cx, cy, dx, dy;
        cin >> ax >> ay >> bx >> by >> cx >> cy >> dx >> dy;
        XY AB = make_pair(ax-bx, ay-by);
        XY CD = make_pair(cx-dx, cy-dy);
        if (para(AB, CD)) cout << "YES" << endl;
        else cout << "NO" << endl;
    }
    return 0;
}

C++: #include <iostream>
using namespace std;
 
int main() {
    int N;
    double x1,y1,x2,y2,x3,y3,x4,y4;
    cin >> N;
    for (int n = 0; n != N; ++n) {
        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 <cassert>
#include <iostream>
#include <vector>

struct Point
{
    double x;
    double y;
};
struct Line
{
    Line(const Point& a, const Point& b)
    : p1(a), p2(b) {}
    Point p1;
    Point p2;
};
double GetSlope(const Line& line)
{
    return
    (line.p2.y - line.p1.y) /
    (line.p2.x - line.p1.x);
}
bool IsParallel(const Line& l1, const Line&l2)
{
    return GetSlope(l1) == GetSlope(l2);
}
bool IsParallel(const std::vector<Point>& points)
{
    assert(points.size() == 4);
    return IsParallel(Line(points[0], points[1]), Line(points[2], points[3]));
}
std::vector<Point> Input(std::istream& is)
{
    std::vector<Point> points(4);
    for(int i = 0; i < points.size(); ++i){
        is >> points[i].x >> points[i].y;
    }
    return points;
}
int main()
{
    int n;
    std::cin >> n;
    for(int i = 0; i < n; ++i) {
        std::vector<Point> points = Input(std::cin);
        std::cout << (IsParallel(points) ? "YES" : "NO") << std::endl; 
    }
    return 0;
}

C++: #include<iostream>
using namespace std;
int main()
{
	double x1,y1,x2,y2,x3,y3,x4,y4;
	int n;
	cin>>n;
	int N[100];
for(int i=0;i<n;i++)
{
	cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
	if((y1-y2)/(x1-x2)==(y3-y4)/(x3-x4))
	{
	N[i]=1;
	}
	else
	{
	N[i]=0;
	}
}
for(int j=0;j<n;j++)
{
	if(N[j]=1)
	{
		cout<<"YES"<<endl;
	}
	else if(N[j]=0)
	{
		cout<<"NO"<<endl;
	}
}
return 0;
}

C++: #include<iostream>
using namespace std;
int main(){
  double a[2],b[2],c[2],d[2];
  int n;
  cin >> n;
  for(int i=0;i<n;i++){
    cin >> a[0] >> a[1] >> b[0] >> b[1] >> c[0] >> c[1] >> d[0] >> d[1];
    if(a[0]-b[0]==0&&c[0]-d[0]==0) cout << "YES" << endl;
    else if(a[1]-b[1]==0&&c[1]-d[1]==0) cout << "YES" << endl;
    if(a[0]-b[0]!=0&&c[0]-d[0]!=0){
      bool ok = false;
      if((b[1]-a[1])/(b[0]-a[0])==(d[1]-c[1])/(d[0]-c[0])){
	cout << "YES" << endl;
	ok = true;
      }
      if(!ok) cout << "NO" << endl;
    }
    else cout << "NO" << endl;
  }   
  return 0;
}

C++: #include <stdio.h>
struct point{
    double x;
    double y;
};
int main(){
    int n;
    point a[4];
    scanf("%d",&n);
    for(int i=0;i<n;i++){
        for(int j=0;j<4;j++){
            scanf("%lf%lf",&a[j].x,&a[j].y);
        }
        if(a[1].x==a[0].x){
            if(a[3].x==a[2].x)printf("YES\n");
            else printf("NO\n");
        }
else  if(a[1].y==a[0].y){
            if(a[3].y==a[2].y)printf("YES\n");
            else printf("NO\n");
        }
else  if(a[3].x==a[2].x){
            if(a[1].x==a[0].x)printf("YES\n");
            else printf("NO\n");
        }
 else if(a[3].y==a[2].y){
            if(a[1].y==a[0].y)printf("YES\n");
            else printf("NO\n");
        }
        else if(((a[1].x-a[0].x)/(a[1].y-a[0].y))==((a[3].x-a[2].x)/(a[3].y-a[2].y)))printf("YES\n");
        else printf("NO\n");
    }
}

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

int main(){
	int n;
	double t[100][8];
	cin >> n;
	for(int i = 0; i < n; i++){
		for(int j = 0; j < 8; j++){
			cin >> t[i][j];
		}
	}
	for(int i = 0; i < n; i++){
		if(t[i][0] == t[i][2]){
			if(t[i][4] == t[i][6]){
				cout << "YES" << endl;
			}
			else{
				cout << "NO" << endl;
			}
		}
		else if(t[i][1] == t[i][3]){
			if(t[i][5] == t[i][7]){
				cout << "YES" << endl;
			}
			else{
				cout << "NO" << endl;
			}
		}
		else if((t[i][1]-t[i][3])/(t[i][0]-t[i][2]) == (t[i][5]-t[i][7])/(t[i][4]-t[i][6])){
			cout << "YES" << endl;
		}
		else{
			cout << "NO" << endl;
		}
	}
}

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

int main(){

	typedef struct{
		double x, y;
	}_td;

	int n;
	_td p1, p2, p3, p4, v_ab, v_cd;
	double del, eps;
	eps = 0.000001;
	
	cin >> n;
	
	for(int i=0; i<n; i++){
		cin >> p1.x >> p1.y >> p2.x >> p2.y >> p3.x >> p3.y >> p4.x >> p4.y;
	
		v_ab.x = p1.x - p2.x;
		v_ab.y = p1.y - p2.y;
		v_cd.x = p3.x - p3.y;
		v_cd.y = p4.x - p4.y;
		
		del = v_ab.x * v_cd.y - v_ab.y * v_cd.x;
		if(abs(del) < eps) cout << "YES" << endl;
		else cout << "NO" << endl;
	}

	return 0;

}