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)
		}
		if fpoints[0] == fpoints[2] && fpoints[4] == fpoints[6] {
			fmt.Println("YES")
			continue
		}
		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>

using namespace std;

bool get_line( double x1 , double x2 , double y1 , double y2 , double& a , double& b );

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

	double a1, a2;
	double b1, b2;

	bool result1 , result2;

	int num;

	cin >> num;

	for( int i = 0 ; i < num ; i++ )
	{
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;

		result1 = get_line( x1 , x2 , y1 , y2 , a1 , b1 );
		result2 = get_line( x3 , x4 , y3 , y4 , a2 , b2 );

		if( result1 == false && result2 == false ) cout << "YES" << endl;

		else
		{
			if( a1 == a2 ) cout << "YES" << endl;
			else cout << "NO" << endl;
		}
	}

	return 0;
}

bool get_line( double x1 , double x2 , double y1 , double y2 , double& a , double& b )
{
	// if( x1 - x2 >= -0.0000001 && x1 - x2 <= 0.0000001 ) return false;

	if( x1 == x2 ) return false;
	else
	{
		a = ( y1 - y2 ) / ( x1 - x2 );
		b = y1 - a * x1;
		return true;
	}
}

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



int main(){

  int num;
  cin >> num;

  double x[4], y[4];
  double xx, yy;
  int i = 0;

  while( i < num ){
  for( int j = 0; j < 4; j++ ){
    cin >> x[j] >> y[j];
  }
  if((y[1]- y[0]) / (x[1] - x[0]) == (y[3] - y[2]) / (x[3] - x[2]) ){
    cout <<"YES"<< endl;
  }else{
    cout <<"NO"<< endl;
  }
  i++;
  }

 
  return 0;
}

C++: #include <algorithm>
#include <vector>
#include <math.h>
#include <stdio.h>
#include <cctype>
#include <iostream>
#include <set>
#include <string>
#include <queue>
#include <map>
#include <utility>
using namespace std;
int size(string x){
	string::size_type size=x.size();
	return size;
}
#define fu(l,k) for(int i=l;i<k;i++)
#define fd(l,k) for(int i=l;i>k;i--)
#define sort(ss) sort(ss.begin(), ss.end())
#define rsort(ss) sort(ss.rbegin(), ss.rend())
typedef  vector<string> vs;
typedef  vector<int> vi;
double pi(){
	return acos(-1.0);
}
typedef set<int> set_i;
typedef set<string> set_s;
int INF=1000000;
int main(){
	int n,ans;
	double x1,x2,x3,x4,y1,y2,y3,y4;
	double ab,cd;
	cin>>n;
	ans=0;
	for(int i=0;i<n;i++){
		cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
		if(x1-x2!=0.0) ab=(y1-y2)/(x1-x2);
		else ab=INF;
		if(x3-x4!=0) cd=(y3-y4)/(x3-x4);
		else cd=INF;
		if(ab==cd) cout<<"YES"<<endl;
		else cout<<"NO"<<endl;
	}
}

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 <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <climits>
#include <queue>

using namespace std;

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;

//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-5;
const double PI  = acos(-1.0);

int main(){
  cin.tie(0);
  ios_base::sync_with_stdio(false);

  int N; cin >> N;
  REP(n,N){
	double x[4], y[4];
	REP(i,4)
	  cin >> x[i] >> y[i];
	x[0] -= x[1], y[0] -= y[1], x[2] -= x[3], y[2] -= y[3];

	if(x[0]*y[2]-x[2]*y[0] < EPS)
	  cout << "YES" << endl;
	else
	  cout << "NO" << endl;
  }
  
  return 0;
}

C++: #include <iostream>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <algorithm>
#include <stdlib.h>
#include <vector>
#include <utility>
#include <queue>
#include <stack>

using namespace std;
int INF = 99999999;
int main(){

	int n;
	cin >> n;

	double x1, y1, x2, y2, x3, y3, x4, y4;

	for(int i=0 ; i<n ; i++){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;

		double steep1, steep2;

		if(y1 == y2){
			steep1 = 0;
		}else if(x1==x2){
			steep1 = INF;
		}else{
			steep1 = (x2-x1)/(y2-y1);
		}

		if(y3==y4){
			steep2 = 0;
		}else if(x3==x4){
			steep2 = INF;
		}else{
			steep2 = (x4-x3)/(y4-y3);
		}

		if(steep1 == steep2) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	return 0;
}

C++: #include<iostream>
#include<string>
#include<algorithm>
#include<map>
#include<vector>
#include<cmath>
#include<cstdio>
#define loop(i,a,b) for(int i=a;i<b;i++) 
#define rep(i,a) loop(i,0,a)
#define pb(in,tmp) in.push_back(tmp)
#define all(in) in.begin(),in.end()
const double PI=acos(-1);
using namespace std;
int main(){
  int n;
  double x[4],y[4];
  cin>>n;
  rep(i,n){
    rep(j,4){
      cin>>x[j];
      cin>>y[j];
    }

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