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
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <queue>
#include <iterator>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>

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 long long LL;
typedef unsigned long long ULL;

//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
//--------------------------------------------
const double EPS = 1e-10;
const double PI  = acos(-1.0);

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

//debug
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

int gcd(int a, int b){
   int tmp;
   while(a%b==0){
      tmp=a%b;
      a=b;
      b=tmp;
   }
}

int lcm(int a,int b){
   return a*b/gcd(a,b);
}

bool prime_number(int n){
   if(n < 2){
      return false;
   }
   else if(n == 2){
      return true;
   }
   if(n % 2 == 0){
      return false;
   }
   for(int i=3;i<=n/i;i+=2){
      if(n % i == 0) return false;
      return true;
   }
}

int main(){
   int n;
   long double x[4],y[4];
   cin >> n;
   REP(i,n){
      REP(j,4) cin >> x[j] >> y[j];
      if((x[1]-x[0])/(y[1]-y[0])==(x[3]-x[2])/(y[3]-y[2])) cout << "YES" << endl;
      else cout << "NO" << endl;
   }
}

C++: 
#include <iostream>
#include <stdio.h>
#include <fstream>
#include <algorithm>
#include <string>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <vector>
#include <limits.h>
#include <math.h>
#define rep(i,n) for (int i = 0; (i) < (n); ++ (i))
using namespace std;

int main(void){
    int n;
    double x[4],y[4],a,b,c,d,det;
    cin >> n;
    rep(j,n) {

    
    //入力を多少簡略化
    for(int i=0;i<4;i++) {
        cin >> x[i] >> y[i];
    }
    //(x1,y1)(x2,y2)を結ぶax+by=p の係数
    a = y[0]-y[1];  b = x[1]-x[0];
    //(x3,y3)(x4,y4)を結ぶcx+dy=q の係数
    c = y[2]-y[3];  d = x[3]-x[2];
    //係数についての行列式
    det = a*d-c*b;
    if(fabs(det) < 0.0001) cout << "YES" << endl;
    else cout << "NO" << endl;
    }
}

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


int main(){
	int n;
	double x1, y1;
	double x2, y2;
	double x3, y3;
	double x4, y4;

	cin >> n;
	for(int i = 0;i < n;i++){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		double xa = x2 - x1, ya = y2 - y1;
		double xc = x4 - x3, yc = y4 - y3;
		double cp = xa*yc - xc*ya;
		if(abs(cp) < 0.00001) cout << "YES" << endl;
		else cout << "NO" << endl;
	}

	return 0;
}

C++: #include <iostream>
#include <complex>
#include <cmath>
#include <cstdio>
using namespace std;
typedef complex<double> xy_t;
const double eps = 1e-11;

double dot_product(xy_t a, xy_t b) { return (conj(a) * b).real(); }
double cross_product(xy_t a, xy_t b) { return (conj(a) * b).imag(); }
xy_t projection(xy_t p, xy_t b) { return b * dot_product(p, b) / norm(b); }

int main()
{
    int n = 0;
    double x, y;
    xy_t P[4];
    double sum = 0.0;
    cin >> n;
    bool answer[n] = {};
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < 4; j++)
        {
            cin >> x >> y;
            P[j] = xy_t(x, y);
        }
        xy_t a[2] = {P[1] - P[0], P[3] - P[2]};
        if (abs(cross_product(a[0], a[1])) < eps)
        {
            answer[i] = 1;
        }
    }
    for (int i = 0; i < n; i++)
    {
        if (answer[i])
        {
            cout << "YES" << endl;
        }
        else
        {
            cout << "NO" << endl;
        }
    }
    return 0;
}

C++: #include <iostream>
#include <complex>
#include <cmath>
using namespace std;
 
double cross(complex<double> z1, complex<double> z2) {
    return (z1.real()*z2.imag() - z1.imag()*z2.real());
}
 
int main(int argc, char** argv) {
    static const double EPS = 1e-10;
    int n;
    cin >> n;
    for(int i=0; i<n; i++) {
        double x[4], y[4];
        for(int j=0; j<4; j++) {
            cin >> x[j] >> y[j];
        }
        complex<double> ab(x[1]-x[0], y[1]-y[0]);
        complex<double> cd(x[3]-x[2], y[3]-y[2]);
        if(abs(cross(ab, cd)) < EPS) { // ?????????0????????????
            cout << "YES" << endl;
        }else {
            cout << "NO" << endl;
        }
    }
}

C++: #include <iostream>

using namespace std;
 
int main(){
  double a,b,c,d,e,f,g,h;
  int t;
  
  cin >> t;
  while(t--){
    cin >> a >> b >> c >> d >> e >> f >> g >> h;
    cout << ((d-b)/(c-a) == (h-f)/(g-e) ? "Yes" : "No") << endl;
  }
 
  return 0;
}

C++: #include <iostream>
#include <stdio.h>
#include <vector>
#include <string>
#include <queue>
#include <map>
#include <algorithm>
#define INF 10000000
using namespace std;
typedef pair<int,int> P;

bool check(double x1,double y1,double x2,double y2){
  return (x1*y2-y1*x2)==0;
}

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(check(x2-x1,y2-y1,x4-x3,y4-y3)){
      cout << "YES" << endl;
    }else{
      cout << "NO" << endl;
    }
  }
}

C++: #include <bits/stdc++.h>
#define rep(i,l,n) for(int i=l;i<n;i++)
using namespace std;

int main(){
	int n;
	cin>>n;
	rep(i,0,n){
		int ans=0;
		double x1,y1,x2,y2,x3,y3,x4,y4,m1,m2;
		cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
		if(x1==x2||x3==x4){
			if(x1==x2&&x3==x4) ans=1;
		}else{
			m1=(y2-y1)/(x2-x1);
			m2=(y4-y3)/(x4-x3);
			if(fabs(m1-m2)<(1e-10)) ans=1;
		}
		if(ans)	cout<<"YES"<<endl;
		else cout<<"NO"<<endl;
	}
}