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>
#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-9;
// 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 = x2 - x1, t = y2 - y1, u = x4 - x3, v = y4 - y3;
		 if (s * v - t * u < EPS) {
			 PRINT("YES");
		 } else {
			 PRINT("NO");
		 }
	}

	return 0;
}

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

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

int main() {
	int N;
	double x[4],y[4];
	cin>>N;
	while(N--){
		for(int i=0;i<4;i++) cin>>x[i]>>y[i];
		double a1=y[1]-y[0];
		a1/=x[1]-x[0];
		double a2=y[3]-y[2];
		a2/=x[3]-x[2];
		if(a1==a2) cout<<"YES"<<endl;
		else cout<<"NO"<<endl;
	}
	return 0;
}

C++: #include <iostream>
#include <cmath>
#define VLN 0.0000000000001
using namespace std;

int main(){
	double N,X[5],Y[5];
	cin>>N;
	for(int j=1;j<=N;j++){
		for(int i=1;i<=4;i++){
			cin>>X[i]>>Y[i];
		}
		if(abs((X[2]-X[1])*(Y[4]-Y[3])-(X[4]-X[3])*(Y[2]-Y[1]))<VLN){
			cout<<"YES"<<endl;
		}
		else{
			cout<<"NO"<<endl;
		}
	}
	return 0;
}

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;
   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 <vector>
#include <string>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <algorithm>	// require sort next_permutation count __gcd reverse etc.
#include <cstdlib>	// require abs exit atof atoi 
#include <cstdio>		// require scanf printf
#include <functional>
#include <numeric>	// require accumulate
#include <cmath>		// require fabs
#include <climits>
#include <limits>
#include <cfloat>
#include <iomanip>	// require setw
#include <sstream>	// require stringstream 
#include <cstring>	// require memset
#include <cctype>		// require tolower, toupper
#include <fstream>	// require freopen
#include <ctime>		// require srand
#define rep(i,n) for(int i=0;i<(n);i++)
#define ALL(A) A.begin(), A.end()
#define EPS 1e-9

using namespace std;

typedef long long ll;
typedef pair<int, int> P;

/*
	この解答は、どうやら誤差死。
	長さを求める平方根と
	掛け算とで誤差が出る模様。
	
	double の計算のときには
	如何に計算しないかがカギ。
*/

double dot (double xa, double ya, double xb, double yb )
{
	return (xa*xb + ya*yb );
}

double calc_len (double x, double y )
{
	return (x*x + y*y );
}

int main()
{
//	cut here before submit 
//	freopen ("testcase.Parallelism", "r", stdin );
	int n;
	scanf ("%d", &n );
	rep (i, n ){
		double x1, y1, x2, y2, x3, y3, x4, y4;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		double d = dot (x2-x1, y2-y1, x4-x3, y4-y3 );
		double len1 = calc_len (x2-x1, y2-y1 );
		double len2 = calc_len (x4-x3, y4-y3 );

		if (fabs (len1*len2 - fabs(d*d ) ) < EPS ){
			cout << "YES" << endl;
		}else{
			cout << "NO" << endl;
		} // end if
	} // end loop
		
	return 0;
}

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

int main()
{
    int n;
    cin>>n;
    for(int i=0;i<n;i++){
        pair<double,double>a[4];
        for(int i=0;i<4;i++){
            cin>>a[i].first>>a[i].second;
        }
        if((a[1].first-a[0].first)==0&&(a[3].first-a[2].first)==0)cout<<"NO"<<endl;
        else if((a[1].second-a[0].second)/(a[1].first-a[0].first)!=(a[3].second-a[2].second)/(a[3].first-a[2].first))
            cout<<"NO"<<endl;
        else cout<<"YES"<<endl;
    }
    return 0;
}

C++: #include<cstdio>

int main(){

    int n;
    scanf("%d",&n);

    for(int i=0;i<n;i++){
        double x1,y1,x2,y2,x3,y3,x4,y4;
        scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);

        if((y2-y1)/(x2-x1)==(y4-y3)/(x4-x3)) printf("YES\n");
        else printf("NO\n");
    }
}