Go: package main

import "fmt"

func abs(x float64) float64 {
	if x < 0 {
		return -x
	}
	return x
}

func main() {
	var n int
	var x1, y1, x2, y2, x3, y3, x4, y4 float64
	fmt.Scan(&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)
		if abs((x2-x1)*(y4-y3) - (y2-y1)*(x4-x3)) < 1e-10 {
			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 if(y[0]==y[1]&&y[2]==y[3]) cout << "NO" << endl;
      else cout << "NO" << endl;
   }
}

C++: w#include<iostream>
#include<iomanip>
#include<vector>
#include<queue>
#include<list>
#include<stack>
#include<algorithm>
#include<cmath>
#include<memory>
#include<array>

using namespace std;

int main()
{
  array<double, 4> x;
  array<double, 4> y;

  int n;
  cin >> n;

  for ( auto j = 0; j < n; ++j )
    {
      for ( auto i = 0; i < 4; ++i )
        {
          cin >> x[i];
          cin >> y[i];
        }
      
      double abx = x[1] - x[0];
      double aby = y[1] - y[0];
      double cdx = x[3] - x[2];
      double cdy = y[3] - y[2];
      
      if ( abx * cdy - aby * cdx == 0 )
        cout << "YES" << endl;
      else
        cout << "NO" << endl;
    }
  
  return 0;
}

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

using P = complex<long long>;

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

string adj(string num) {
    int cnt = 0;
    while (cnt < num.size() && num[cnt] != '.') cnt++;
    if (cnt == num.size()) {
	num += ".00000";
    }
    else {
	int len = num.size() - 1 - cnt;
	for (int i = 0; i < 5 - len; i++) num += '0';
    }
    return num;
}


long long pr(string num) {
    num = adj(num);
    long long ans = 0;
    for (int i = 0; i < num.size(); i++) {
	if ('0' <= num[i] && num[i] <= '9') {
	    ans = ans * 10 + num[i] - '0';
	}
    }
    if (num[0] == '-') ans = -ans;
    return ans;
}

int main() {
    int n;
    cin >> n;
    while (n--) {
	P pp[4];
	for (int i = 0; i < 4; i++) {
	    string x, y;
	    cin >> x >> y;
	    pp[i] = P(pr(x), pr(y));
	}
	if (cross(pp[1] - pp[0], pp[3] - pp[2]) == 0) {
	    cout << "YES" << endl;
	}
	else {
	    cout << "NO" << endl;
	}
    }
    return 0;
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <numeric>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <utility>
#include <sstream>
#include <complex>

using namespace std;

#define FOR(i,a,b) for(long long i=(a);i<(b);i++)
#define REP(i,N) for(long long i=0;i<(N);i++)
#define ALL(s) (s).begin(),(s).end()
#define fi first
#define se second

#define PI acos(-1.0)
#define INF 1000000007

typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<double, double> PD;
typedef pair<string, ll> PS;
typedef vector<ll> V;

int n;
double x[100], y[100];

int main(){
	cin >> n;
	REP(i, n){
		REP(j, 4) cin >> x[j] >> y[j];
		if (fabs((x[1] - x[0])*(y[3] - y[2]) 
			- (x[3] - x[2])*(y[1] - y[0]))<1e-10){
			cout << "YES" << endl;
		}
		else{
			cout << "NO" << endl;
		}
	}
	return 0;
}

C++: #include <algorithm>
#include <functional>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <vector>
#include <list>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <bitset>
#include <climits>

#define all(c) (c).begin(), (c).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define pb(e) push_back(e)
#define mp(a, b) make_pair(a, b)
#define fr first
#define sc second

const int INF=100000000;
int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};
using namespace std;
typedef pair<int ,int > P;
typedef long long ll;

int n;
int main() {
    cin>>n;
    double x1,y1;
    double x2,y2;
    double x3,y3;
    double x4,y4;
    rep(i,n) {
        cin>>x1>>y1;
        cin>>x2>>y2;
        cin>>x3>>y3;
        cin>>x4>>y4;
        double tx1 = x1-x2 + 1e-8;
        double ty1 = y1-y2 + 1e-8;
        double tx2 = x3-x4 + 1e-8;
        double ty2 = y3-y4 + 1e-8;

        if(tx1*ty2==tx2*ty1) {
            cout<<"YES"<<endl;
        }
        else {
            cout<<"NO"<<endl;
        }

    }
    return 0;
}

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

int main ()
{
	int n;
	cin>>n;
	for(int h=0;h<n;h++)
	{
		double x[4],y[4];
		for(int i=0;i<4;i++)cin>>x[i]>>y[i];
		if(x[0]==x[1]||x[2]==x[3])
		{
			if(x[0]==x[1]&&x[2]==x[3])
			{
				cout<<"YES"<<endl;
			}
			else
			{
				cout<<"NO"<<endl;
			}
		}
		else if(y[1]-y[0]==0||y[3]-y[2]==0)
		{
			if(y[1]-y[0]==0&&y[3]-y[2]==0)
			{
				cout<<"YES"<<endl;
			}
			else cout<<"NO"<<endl;
		}else
		{
			double Z,X;
			Z=(y[1]-y[0])/(x[1]-x[0]);
			X=(y[3]-y[2])/(x[3]-x[2]);
			if(Z==X)
			{
				cout<<"YES"<<endl;
			}
			else cout<<"NO"<<endl;
		
		}
	}
	
}