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<algorithm>
#include<vector>
#include<stack>
#include<queue>
#include<cstdio>
#include<climits>
#include<cmath>
#include<cstring>
#include<string>
#include<complex>
#include<cfloat>
#include<cassert>

#define f first
#define s second
#define mp make_pair

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,c) for(__typeof((c).begin()) i=(c).begin(); i!=(c).end(); i++)
#define ALL(c) (c).begin(), (c).end()
#define EPS (1e-10)
using namespace std;

typedef unsigned int uint;
typedef long long ll;
typedef complex<double> P;

#define PI (3.1415926535)
#define EPS (1e-10)

bool eq(double a, double b){
  return abs(a-b) < EPS;
}

int main(){
  int n; cin>>n;
  while(n-->0){
    P p[4];
    REP(i,4) cin>>p[i].real()>>p[i].imag();
    P a,b;
    a = p[0] - p[1];
    b = p[2] - p[3];
    
    if(eq(arg(a),arg(b)) || eq(arg(a),arg(-b)))
      cout << "YES" << endl;
    else
      cout << "NO" << endl;
      
  }
  
  return 0;
}

C++: #include<stdio.h>
#include<math.h>
int main(void)
{
	int n;
	int i,j;
	double x[5],y[5];
	double xx,yy;
	
	scanf("%d",&n);
	for(i=0;i<n;i++){
		for(j=0;j<4;j++){
			scanf("%lf %lf",&x[j],&y[j]);
		}
		if(x[0]-x[1]==0 || x[2]-x[3]==0){
			if(x[0]-x[1]==0 && x[2]-x[3]==0){
				printf("YES\n");
			}
			else {
				printf("NO\n");
			}
		}
		else {
			xx=(double)(y[0]-y[1])/(x[0]-x[1]);
			yy=(double)(y[2]-y[3])/(x[2]-x[3]);
	//		printf("%lf %lf\n",xx,yy);
			if(xx==yy){
				printf("YES\n");
			}
			else {
				printf("NO\n");
			}
		}
	}	
	return 0;
}

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

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

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

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

class vec2d {
public:
  double x,y;
  void set(double x=0,double y=0) {
    this->x = x;
    this->y = y;
  }
};
double cross(vec2d A,vec2d B) {
  return (A.x*B.y - B.x*A.y);
}
bool is_paralles(vec2d A,vec2d B) {
  if(cross(A,B) < 1e-9) return true;
  return false;
}

int main() {
  int n;
  vec2d AB,CD;
  double x1,y1,x2,y2,x3,y3,x4,y4;
  cin >> n;
  for(int i=0;i<n;i++) {
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
    AB.set(x2-x1,y2-y1);
    CD.set(x4-x3,y4-y3);
    if(is_paralles(AB,CD)) {
      cout << "YES" << endl;
    }
    else {
      cout << "NO" << endl;
    }
  }
}

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

int main(){
	int n;
	double t[100][8];
	double ab, cd;
	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++){
		ab = (t[i][1]-t[i][3])*(t[i][4]-t[i][6]);
		cd = (t[i][5]-t[i][7])*(t[i][0]-t[i][2]);
		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(ab == cd){
			cout << "YES" << endl;
		}
		else{
			cout << "NO" << endl;
		}
	}
}

C++: #include<iostream>
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(a==c||e==g)cout<<(a==c&&e==g?"YES":"NO")<<endl;
		else cout<<((d-b)/(c-a)==(h-f)/(g-e)?"YES":"NO")<<endl;
	}
}