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)
		}
		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>
#define REP(i,n) for(int i = 0; i < (n); ++i)
using namespace std;

int main(){
	int n;
	cin >> n;
	double x1,y1,x2,y2,x3,y3,x4,y4;
	REP(i,n){
		cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
		double a0 = (y2-y1) / (x2-x1), a1 = (y4-y3) / (x4-x3);
		if(a0 == a1) 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;
	//ごみ
	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( (y1-y2)==0 || (y3-y4)==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>
#include <algorithm>
#include <vector>
#include <math.h>
#include <cmath>
#include <utility>
#include <queue>
#include <stdio.h>
#include <string>
#include <map>
#include <stack>
#include <complex>
#define rep(i,n) for(int i=0;i<n;i++)
#define INF 1000000000007
const double eps = 1e-11;
using namespace std;
typedef long long int ll;
typedef complex<double> xy;

int main(){
    int n;
    cin >> n;
    for (int j=0; j<n; j++) {
        vector<xy> inp;
        double x,y,z,w;
        for (int i=0; i<2; i++) {
            cin >> x >> y >> z >> w;
            inp.push_back(xy(x-z,y-w));
        }
        double ans;
        ans =((conj(inp[0])*inp[1]).imag());
        bool b = abs(ans) < eps;
        cout << (b ? "YES" : "NO")<<endl;
    }
}

C++: #include <cstdio>
#include <complex>
#include <vector>

using namespace std;

typedef complex<double> P;
struct L : public vector<P> {
    L(const P &a, const P &b) {
        push_back(a);
        push_back(b);
    }
};

const double EPS = 1e-8;

int cross(P a, P b)
{
    return imag(conj(a) * b);
}

bool intersectLL(const L &l, const L &m)
{
    return abs(cross(l[1]-l[0], m[1]-m[0])) > EPS;
}

int main()
{
    int n;

    scanf("%d", &n);
    for (int i = 0; i < n; ++i) {
        P p[4];
        double x, y;

        scanf("%lf %lf", &x, &y);
        p[0] = P(x, y);
        scanf("%lf %lf", &x, &y);
        p[1] = P(x, y);
        scanf("%lf %lf", &x, &y);
        p[2] = P(x, y);
        scanf("%lf %lf", &x, &y);
        p[3] = P(x, y);

        puts(intersectLL(L(p[0], p[1]), L(p[2], p[3])) ? "NO" : "YES");
    }

    return 0;
}

C++: /**
 * 
 */
import java.util.*;
/**
 * @author afterCmidday
 *
 */
class Main {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		final double eps = 1e-10;
		int n;
		Scanner scan = new Scanner(System.in);
		n = scan.nextInt();
		for(int i = 0;i < n;i++){
			double x1 = scan.nextDouble(), y1 = scan.nextDouble(), x2 = scan.nextDouble(), y2 = scan.nextDouble();
			double a = x2 - x1, b = y2 - y1;
			double x3 = scan.nextDouble(), y3 = scan.nextDouble(), x4 = scan.nextDouble(), y4 = scan.nextDouble();
			double c = x4 - x3, d = y4 - y3;
			double e = a * d - b * c;
			if(Math.abs(e) < eps){
				System.out.println("YES");
			}else{
				System.out.println("NO");
			}
		}

	}

}

C++: #include <iostream>

using namespace std;

int main()
{
	double x1, y1, x2, y2, x3, y3, x4, y4;
	int N;
	cin >> N;
	
	for (int i=0; i<N; i++) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		
		if ( ( (x1==x2) && (y1==y2) ) || ( (x3==x4) && (y3==y4) ) ) {
			cout << "NO" << endl;
			continue;
		}
		
		double LHS = 1000000.0 * (y2 - y1) * (x4 - x3);
		double RHS = 1000000.0 * (y4 - y3) * (x2 - x1);
		//cout << LHS << " " << RHS << endl;
		//if ( (y2 - y1) * (x4 - x3) == (y4 - y3) * (x2 - x1) ) cout << "YES" << endl;
		if ( LHS == RHS ) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
		
	return 0;
}

C++: #include<cstdio>
#include<iostream>
#include<algorithm>
#include<vector>
#include<set>
#include<string>
#include<functional>
#include<queue>
#include<stack>
#include<math.h>
#define INF 999999
#define EPS 1.0e-6

using namespace std;

typedef long long ll;


int main()
{
	int n;
	cin >> n;
	double x1, y1, x2, y2, x3, y3, x4, y4;
	for(int i=0;i<n;i++){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		double a = (y2 - y1)*(x4 - x3) - (y4 - y3)*(x2 - x1);
		if (fabs(a) < EPS )printf("YES\n");
		else printf("NO\n");
	}
	
	return 0;
}

C++: #include <iostream>
#include <string>
#include <cctype>
#include <cmath>
#include <stdio.h>
#include <algorithm>
#include <vector>
#include <map> // pair
#include <set>
#include <string>

#define MAXSIZE 200000
#define PI 3.141592653589
using namespace std;

template<typename T>
T add(T a,T b){
  return a+b;
}

namespace A
{
  int f(void){
    return 1;
  }
}


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

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

    if(abs((x1-x2)*(y3-y4)-(x3-x4)*(y1-y2))<0.000001){
      std::cout << "YES" << '\n';
    }else{
      std::cout << "NO" << '\n';
    }
  }
}

C++: #include <iostream>

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

const int INF = 10000000;
using namespace std;
typedef long long  ll;
const int MAX = 10000;

/** Problem0021 : Parallelism **/
int main()
{
	int n;
	cin >> n;
	rep(k, n) {
		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" << endl;
		else
			cout << "NO" << endl;
	}
	return 0;
}

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

using namespace std;
typedef long long ll;

int main(){
    
    int n = 0;
    cin >> n;

    float Ax, Ay, Bx, By, Cx, Cy, Dx, Dy;
    vector<pair<float, float> > A;
    vector<pair<float, float> > B;
    vector<pair<float, float> > C;
    vector<pair<float, float> > D;

    for(int i = 0; i < n; i++){
        cin >> Ax >> Ay >>  Bx >>  By >>  Cx >>  Cy >>  Dx >> Dy;
        A.push_back(make_pair(Ax, Ay));
        B.push_back(make_pair(Bx, By));
        C.push_back(make_pair(Cx, Cy));
        D.push_back(make_pair(Dx, Dy));
    }

    for(int i = 0; i < n; i++){
        float a = 0;
        float b = 0;
        //0除算対策
        if(A[i].first == B[i].first ){
            a = 9999999;
        }else{
            a = (A[i].second - B[i].second) / (A[i].first - B[i].first);
        }

        if(C[i].first == D[i].first){
            b = 9999999;
        }else{
             b = (C[i].second - D[i].second) / (C[i].first - D[i].first);
        }

        if(a == b){
            cout << "YES" << endl;
        }else{
            cout << "NO" << endl;
        }
    }
}