Go: package main

import (
	"bufio"
	"os"
	"strconv"
	"fmt"
	"strings"
)

var scanner = bufio.NewScanner(os.Stdin)

func nextInt() int {
	scanner.Scan()
	i, e := strconv.Atoi(scanner.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func main() {
	n := nextInt()
	for i := 0; i < n; i++ {
		scanner.Scan()
		points := strings.Split(scanner.Text(), " ")
		fpoints := make([]float64, 0)
		for _, v := range points {
			tmp, _ := strconv.ParseFloat(v, 64)
			fpoints = append(fpoints, tmp)
		}
		if fpoints[0] == fpoints[2] && fpoints[4] == fpoints[6] {
			fmt.Println("YES")
			continue
		}
		a := (fpoints[1]-fpoints[3])/(fpoints[0]-fpoints[2])
		b := (fpoints[5]-fpoints[7])/(fpoints[4]-fpoints[6])
		if a == b {
			fmt.Println("YES")
		} else {
			fmt.Println("NO")
		}
	}
}

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

#define REP(i, s, n) for (int i = s; i < n; ++i)
#define rep(i, n) REP(i, 0, n)
#define SORT(c) sort((c).begin(), (c).end())
#define IINF INT_MAX
#define LLINF LLONG_MAX
#define DEBUG false

int main()
{
    int n;
    pair<double, double> pa;
    vector<pair<double, double> > a;
    vector<pair<double, double> > b;
    cin >> n;
    rep(j, n)
    {
        rep(i, 2)
        {
            cin >> pa.first;
            cin >> pa.second;
            a.push_back(pa);
        }
        rep(i, 2)
        {
            cin >> pa.first;
            cin >> pa.second;
            b.push_back(pa);
        }
        SORT(a);
        SORT(b);
        double anglea = (a[1].second - a[0].second)*(b[1].first - b[0].first);
        double angleb = (b[1].second - b[0].second)*(a[1].first - a[0].first);
        if(DEBUG) cout<<anglea<<" "<<angleb<<endl;
        if (anglea==angleb)
        {
            cout << "YES" << endl;
        }
        else
        {
            cout << "NO" << endl;
        }
        a.clear();
        b.clear();
    }
    return 0;
}

C++: #include <cstdio>

using namespace std;

double x1,y1,x2,y2,x3,y3,x4,y4;
    

int main()
{
    int n; scanf( "%d\n", &n );
    while( n > 0 )
    {
        scanf("%lf %lf %lf %lf %lf %lf %lf %lf\n", &x1, &y1, &x2, &y2, &x3, &y3, &x4, &y4 );
        double dx1 = x2 - x1, dx2 = x4 - x3, dy1 = y2 - y1, dy2 = y4 - y3, det = dx1 * dy2 - dx2 * dy1;

        if( det < 0.000000001 )
        {
            printf( "YES\n" );
        }
        else
        {
            printf( "NO\n" );
        }

        /* if( (dx1 == 0 && dx2 == 0) || (dy1 == 0 && dy2 == 0 ) )
        {
            printf( "YES\n" );
        }
        else if( dx1 != 0 && dx2 != 0 )
        {
            dy1 /= dx1;
            dy2 /= dx2;
            if( dy1 == dy2 || dy1 == -dy2 )
            {
                printf( "YES\n" );
            }
        }
        else
        {
            printf( "NO\n" );
        }
         */
        n--;
    }
    return 0;
}

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

struct TCoordinate
{
	double x;
	double y;
};

struct TLine
{
	TCoordinate StartPoint;
	TCoordinate EndPoint;
	double GetInclination()
	{
		return (EndPoint.y - StartPoint.y) / (EndPoint.x - StartPoint.x);
	}
};

int main()
{
	int n;
	cin >> n;
	for(int i = 0; i < n; i++){
		TLine AB, CD;
		cin >> AB.StartPoint.x >> AB.StartPoint.y
		    >> AB.EndPoint.x   >> AB.EndPoint.y
		    >> CD.StartPoint.x >> CD.StartPoint.y
		    >> CD.EndPoint.x   >> CD.EndPoint.y;
		if(AB.GetInclination() == CD.GetInclination()){
			cout << "YES" << endl;
		}else{
			cout << "NO" << endl;
		}
	}
	return 0;
}

C++: #include <cstdio>
#include <queue>
#include <algorithm>
#include <cmath>

#define rep(i, n) for(int i = 0; i < (n); ++i)

using namespace std;

int n;
double x[4];
double y[4];

int main(){
	scanf("%d", &n);
	rep(i, n){
		rep(j, 4){
			scanf("%lf%lf", x + j, y + j);
		}

		double dx[2];
		double dy[2];
		dx[0] = x[0] - x[1];
		dx[1] = x[2] - x[3];
		dy[0] = y[0] - y[1];
		dy[1] = y[2] - y[3];

		// printf("(%lf, %lf) (%lf, %lf)\n", dx[0], dy[0], dx[1], dy[1]);

		printf("%s\n", dy[0] / dx[0] == dy[1] / dx[1] ? "YES" : "NO");
	}
	return 0;
}

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)
			{
			}
			else 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/y2;
		q=x4/y4;

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

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

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

int main(){
	double x[4], y[4];
	int n, i, j;

	cin >> n;

	for(i = 0; i < n; i ++){
		for(j = 0; j < 4; j ++){
			cin >> x[j] >> y[j];
		}
		x[1] -= x[0];
		y[1] -= y[0];
		x[3] -= x[2];
		y[3] -= y[2];

		if(x[1] == 0 || x[3] == 0){
			if(x[1] == 0 && x[3] == 0){
				printf("YES\n");
			}else{
				printf("NO\n");
			}
			}else{
				if(y[1]/x[1] == y[3]/x[3]){
					printf("YES\n");
				}else{
					printf("NO\n");
			}
		}
	}
	
	return 0;    
}

C++: #include <iostream>
#include <stack>
#include <stdio.h>
#include <math.h>
using namespace std;
double x[4],y[4];//p,1,2,3
double make_line(double x1,double y1,double x2,double y2){
	double a,b,c;//ax+by+c=0
	if(x1!=x2&&y1!=y2){
		a=(y1-y2)/(x1-x2);
		b=-1;
		c=-a*x1+y1;
	}else if(x1==x2){
		a=1;
		b=0;
		c=-x1;
	}else if(y1==y2){
		a=0;
		b=1;
		c=-y1;
	}
	return a;
}
int main()
{
	int n;
	cin>>n;
	while(n--){
		cin>>x[0]>>y[0]>>x[1]>>y[1]>>x[2]>>y[2]>>x[3]>>y[3];
		printf(abs(make_line(x[0],y[0],x[1],y[1])-make_line(x[2],y[2],x[3],y[3]))<=0.000001?"YES\n":"NO\n");
	}
    return 0;
}

C++: #include<iostream>
#include<iomanip>
#include<string>
#include<algorithm>
#include<cmath>
using namespace std;
int main(){
    int n;
    cin>>n;
    float x1,y1,x2,y2,x3,y3,x4,y4;
    for(int i=0;i<n;i++){
        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>

int main(){
  int n;
  double x1,y1,x2,y2,x3,y3,x4,y4;
  const double e = 1e-7;

  std::cin >> n;

  for(int i=0;i<n;i++){
    std::cin >> x1 >> y1
             >> x2 >> y2
             >> x3 >> y3
             >> x4 >> y4;

    if((x1*y3+x2*y4+y2*x3+y1*x4)-(x2*y3+x1*y4+y1*x3+y2*x4)<e){
      std::cout << "YES" << std::endl;
    }else{
      std::cout << "NO" << std::endl;
    }
  }
}