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 <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <functional>
#include <string>
#include <algorithm>
#include <climits>
#include <utility>

#define PRINT(STR) cout << STR << endl;
#define REP(i, n) for (int (i) = 0; (i) < (int)(n); (i)++)
#define REG(i, a, b) for (int (i) = ((int)(a)); (i) < ((int)(b)); i++)
#define ALL(V) (V).begin(), (V).end()

typedef long long ll;

using namespace std;

int nextInt() { int n = -1; cin >> n; return n; }
double nextDouble() { double d = -1; cin >> d; return d; }
ll nextll() { ll n = -1; cin >> n; return n; }
string nextString() { string str; cin >> str; return str; }

int INF = 9999999;
double EPS = 1e-17;
// BEGIN //////////////////////////////////////////////////////////////


int main() {
	int N;
	scanf("%d", &N);
	double x1, y1, x2, y2, x3, y3, x4, y4;
	for (int i = 0; i < N; i++) {
		 scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);
		 double s = x1 - x2, t = y1 - y2, u = x3 - x4, v = y3 - y4;
		 if (s * v == t * u) {
			 PRINT("YES");
		 } else {
			 PRINT("NO");
		 }
	}

	return 0;
}

// END   //////////////////////////////////////////////////////////////

C++: #include <stdio.h>

int main(void) {
  int n, i, j;
  scanf("%d",&n);
  for(i = 0; i < n; ++i) {
    double a[8];
    for(j = 0; j < 8; ++j) scanf("%lf", &a[j]);
    a[3] -= a[1], a[2] -= a[0], a[6] -= a[4], a[7] -= a[5];
    if(a[3] / a[2] == a[7] / a[6] || a[3] / a[2] == -a[7] / a[6]) printf("YES\n");
    else printf("NO\n");
  }
  return 0;
}

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

#define EPS (1e-10)
#define EQ(a,b) (abs((a)-(b)) < EPS)
#define EQV(a,b) ( EQ( (a).real() , (b).real() ) && EQ( (a).imag(), (b).imag() ) )

int main(){
  int n;
  double x1,y1,x2,y2,x3,y3,x4,y4;
  cin>>n;
  while(n--){
    cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
    if( abs( (y2-y1)/(x2-x1) - (y4-y3)/(x4-x3)) <= EPS ){
      cout<<"YES"<<endl;
    }else{
      cout<<"NO"<<endl;
    }
  }
}

C++: #include<iostream>
#include<algorithm>
#include<string>
using namespace std;
int main() {
	int n;
	cin >> n;
	for (int z = 0; z < n; z++) {
		long float x1, x2, x3,y1, y2, y3, y4, x4 ;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		if (y1 > y2) {
			swap(y1, y2);
			swap(x1, x2);
		}
		if (y3 > y4) {
			swap(y3, y4);
			swap(x3, x4);
		}
		if ((x1 > x2&&x3 > x4 && ((y2 - y1) / (x1 - x2) == (y4 - y3) / (x3 - x4))) || (x2 > x1&&x4 > x3 && ((y1 - y2) / (x2 - x1) == (y3 - y4) / (x4 - x3)))) {
			cout << "YES" << endl;
		}
		else {
			cout << "NO" << endl;
		}
	}
}

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

int main() {
	double x1, y1, x2, y2, x3, y3, x4, y4;
	int n;
	double veku1[2];
	double veku2[2];
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		veku1[0] = x2 - x1;
		veku1[1] = y2 - y1;
		veku2[0] = x4 - x3;
		veku2[1] = y4 - y3;
		if (abs(veku1[0]*veku2[1]-veku1[1]*veku2[0]) <= 0.0000001) {
			veku1[0] = x3 - x1;
			veku1[1] = y3 - y1;
			veku2[0] = x4 - x1;
			veku2[1] = y4 - y1;
			if (abs(veku1[0]*veku2[1]-veku1[1]*veku2[0]) <= 0.0000001) {
				cout << "NO" << endl;
			} else {
				cout << "YES" << endl;
			}
		} else {
			cout << "NO" << endl;
		}
	}
	return 0;
}

C++: #include <stdio.h>
#include <cctype>
#include <limits.h>
#include <math.h>
#include <complex>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <cstring>
#include <string>
#include <sstream>
#include <algorithm>
#include <iomanip>
#include <iostream>

#define VARIABLE(x) cerr << #x << "=" << x << endl
#define BINARY(x) static_cast<bitset<16> >(x)
#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++)
#define if_range(x, y, w, h) if (0<=(int)(x) && (int)(x)<(int)(w) && 0<=(int)(y) && (int)(y)<(int)(h))
#define ALL(a) (a).begin(),(a).end()
const int INF = 1e9;
const double PI = 3.14159;
int dx[4]={0, 1, 0, -1}, dy[4]={-1, 0, 1, 0};
using namespace std;
typedef long long ll;
//typedef pair<int, int> P;

/* struct P {
	int x, y, n;
	P(int n, int x, int y):n(n), x(x), y(y){}
	P(){}
}; */


/** 幾何ライブラリ **/
// to do : 1183

#include <complex>

#define X real()
#define Y imag()

const double EPS = 1e-11;

typedef double D;
typedef complex<D> P; // Point

// 共役複素数 conj(a);

// 符号
int sig(D a, D b=0) { return a < b - EPS ? -1 : (a > b + EPS ? 1 : 0); }

// 内積
D dot_product(P a, P b) { return (conj(a)*b).real(); }

// 外積
D cross_product(P a, P b) { return (conj(a)*b).imag(); }

/** Problem0021 : Parallelism **/
int main()
{
	int N; cin>>N;
	rep(i, N) {
		P a, b;
		D x1, y1, x2, y2;
		cin>>x1>>y1>>x2>>y2;
		a.X = (x2 - x1);
		a.Y = (y2 - y1);
		
		cin>>x1>>y1>>x2>>y2;
		b.X = (x2 - x1);
		b.Y = (y2 - y1);
		
		if (abs(cross_product(a, b))<EPS) {
			cout << "YES" << endl;
		} else {
			cout << "NO" << endl;
		}
	}
}

C++: #include <iostream>


using namespace std;

int main()
{
	int i,num;
	float x[4],y[4];
	cin >> num;

	for ( i = 0 ; i< num; i++ ) {
		cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2] >> x[3] >> y[3];

		if( abs( (x[0]-x[1])*(y[2]-y[3]) - (y[0]-y[1])*(x[2]-x[3]) ) < 1e-10 ){
			cout << "YES" << endl;
		}
		else{
			cout << "NO" << endl;
		}
	}
	return 0;
}

C++: #include<iostream>
#include<string>
#include<cmath>
#include<queue>
#include<vector>
#include<functional>
using namespace std;
int main() {
	int n;
	double x1, y1, x2, y2, x3, y3, x4, y4;
	cin >> n;
	for (int z = 0; z < n; z++) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		double a = 99999, b = 99999;
		a = (x2 - x1)*(x4 - x3);
		b = (y2 - y1)*(y4 - y3);
		if (a == b) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
}

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

int main()
{
	int N; cin >> N;
	while(N--)
	{
		double x1,x2,x3,x4,y1,y2,y3,y4;
		cin >> x1 >> y1 >> x2 >> y2;
		cin >> x3 >> y3 >> x4 >> y4;

		x2 -= x1; y2 -= y1;
		x4 -= x3; y4 -= y3;

		cout << (x2*y4-x4*y2<1e-5 ? "YES" : "NO") << (N!=1 ? "" : "\n");

	}
}

C++: #include<iostream>
#include<complex>
#include<cmath>
using namespace std;
#define EPS 1e-10

int main(void){
	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( abs((x2-x1)*(y4-y3) - (x4-x3)*(y2-y1))<EPS )
			cout << "YES" << endl;
		else
			cout << "NO" << endl;
	}
	return 0;
}