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[1] == fpoints[3] {
			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 <iostream> 
#include <cmath> 
#include <iomanip> 
using namespace std;

int main(void) {
    int n;
    cin >> n;
    for(int i = 0; i < n; i++){
        double point[4][2];
        for(int j = 0; j < 4; j++){
            for(int k = 0; k < 2; k++){
                cin >> point[j][k];
            }
        }
        if(((point[1][0] - point[0][0]) / (point[1][1] - point[0][1])) == ((point[3][0] - point[2][0]) / (point[3][1] - point[2][1]))){
            cout << "Yes" << endl;
        }
        else{
            cout << "No" << endl;
        }
    }
    return 0;
}

C++: #define _USE_MATH_DEFINES
#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<cmath>
#include<list>
#include<stack>
#include<queue>
#include<cctype>
#include<iomanip>
#include<functional>
using namespace std;
typedef long long llong;
class Point {
public:
	double x, y;
};
int main() {
	int n; cin >> n;
	while (n--) {
		Point a, b, c, d;
		cin >> a.x >> a.y >> b.x >> b.y >> c.x >> c.y >> d.x >> d.y;
		b.x -= a.x; a.x = 0;
		b.y -= a.y; a.y = 0;
		d.x -= c.x; c.x = 0;
		d.y -= c.y; c.y = 0;
		double z = b.x*d.y - b.y*d.x;
		if (z == 0)cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	return 0;
}

C++: //include
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <fstream>
#include <complex>
using namespace std;

//conversion
//------------------------------------------
inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}

//math
//-------------------------------------------
template<class T> inline T sqr(T x) {return x*x;}

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<long, long> PLL;
typedef long long LL;
//container util
//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

//repetition
//------------------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)

//constant
//--------------------------------------------

//clear memory
#define CLR(a) memset((a), 0 ,sizeof(a))

const double EPS = 1e-8;
const double INF = 1e12;

typedef complex<double> P;
namespace std {
  bool operator < (const P& a, const P& b) {
    return real(a) != real(b) ? real(a) < real(b) : imag(a) < imag(b);
  }
}
double cross(const P& a, const P& b) {
  return imag(conj(a)*b);
}
struct L : public vector<P> {
  L(const P &a, const P &b) {
    push_back(a); push_back(b);
  }
};

bool intersectLL(const L &l, const L &m) {
  return abs(cross(l[1]-l[0], m[1]-m[0])) > EPS || // non-parallel
         abs(cross(l[1]-l[0], m[0]-l[0])) < EPS;   // same line
}

int main(){
	int n;
	cin>>n;
	REP(i,n){
		P p1,p2,p3,p4;
		cin>>p1.real()>>p1.imag()>>p2.real()>>p2.imag()>>p3.real()>>p3.imag()>>p4.real()>>p4.imag();
		L l1(p1,p2),l2(p3,p4);
		if(!intersectLL(l1,l2))cout<<"YES"<<endl;
		else cout<<"NO"<<endl;
	}
	return 0;
}

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

using P = complex<long long>;

int cross(P p1, P p2) {
    return (p1.real() * p2.imag() - p1.imag() * p2.real());
}

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];
	P pp[4];
	for (int i = 0; i < 4; i++) pp[i] = P(x[i] * 100000, y[i] * 100000);
	if (pp[0] == pp[1] || pp[2] == pp[3]) {
	    cout << "NO" << endl;
	}
	else if (cross(pp[1] - pp[0], pp[3] - pp[2]) == 0) {
	    cout << "YES" << endl;
	}
	else {
	    cout << "NO" << endl;
	}
    }
    return 0;
}

C++: #include <iostream>
#include <cmath>
using namespace std;
int main(){
  

  int dataSets;
  cin >> dataSets;
  for(int i=0;i<dataSets;i++){
    double x1, y1, x2, y2, x3, y3, x4, y4;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
    if((abs((y2-y1)*(x4-x3) - (x2-x1)*(y4-y3)) < 0.0001){
      cout << "YES" << endl;
    }else{
      cout << "NO" << endl;
    }
    
  }

  return 0;

}

C++: #define _USE_MATH_DEFINES
 
#include <iostream>
#include <cstdio>
#include <algorithm>
#include <string>
#include <vector>
#include <math.h>

using namespace std;

int main(){
	int n;
	cin >> n;

	for(int i=0;i<n;i++){
		double x1, y1, x2, y2, x3, y3, x4, y4;
		cin >> x1 >>y1 >>x2 >>y2 >>x3 >>y3 >>x4 >>y4;
		
		double t1 = (y1-y2)*(x3-x4);
		double t2 = (y3-y4)*(x1-x2);

		if( (x1-x2)==0 && (x3-x4)==0 ){
			if( (x1-x2)==0 || (x3-x4)==0 ){
				cout << "NO" << endl;
			}else{
				cout << "YES" << endl;
			}
		}else if( (x1-x2)==0 || (x3-x4)==0 ){
			cout << "NO" << endl;
		}else if( t1==t2 ){
			cout << "YES" << endl;
		}else{
			cout << "NO" << endl;
		}
	}

	return 0;
}

C++: #include<iostream>

using namespace std;

int main(){
	int n;
	cin >> n;

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

	while (n--){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		cout << (((y2 - y1) / (x2 - x1) == (y4 - y3) / (x4 - x3)) ? "YES\n" : "NO\n");
	}

	return 0;
}

C++: #include<iostream>
#include<cmath>

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

	return 0;
}

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

int main()
{
    int n;
    cin >> n;

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

        if( ((y2-y1)/(x2-x1)) == ((y4-y3)/(x4-x3)) ) cout << "YES\n";
        else cout << "NO\n";
    }
    return 0;
}