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<iostream>
#include<cstdio>
#include<string>
#include<algorithm>

using namespace std;

int main(){
	int n;
	float x1,x2,x3,x4;
	float y1,y2,y3,y4;
	float a1,a2;
	
	scanf("%d",&n);
	for(int i=0;i<n;i++){
		scanf("%f%f%f%f%f%f%f%f",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);
		a1 = (y2-y1)/(x2-x1);
		a2 = (y4-y3)/(x4-x3);
		if(a1==a2)
		printf("YES\n");
		else
		printf("NO\n");
	}
}

C++: #include<iostream>
using namespace std;
double x[4], y[4], xp[2], yp[2]; int n;
int main() {
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2] >> x[3] >> y[3];
		xp[0] = x[0] - x[1];
		yp[0] = y[0] - y[1];
		xp[1] = x[2] - x[3];
		yp[1] = y[2] - y[3];
		if (yp[0] == 0 && yp[1] == 0) { goto E; }
		if (yp[0] == 0 && yp[1] != 0) { goto F; }
		if (yp[0] != 0 && yp[1] == 0) { goto F; }
		if ((xp[0] / yp[0]) == (xp[1] / yp[1])) { goto E; }
		goto F;
	E:; cout << "YES" << endl;
		goto G;
	F:; cout << "NO" << endl;
	G:;
	}
}

C++: #include<bits/stdc++.h>
using namespace std;
 
signed main(){
int a;
cin>>a;
double c[8];
for(int b=0;b<a;b++){
    for(int d=0;d<8;d++)scanf("%lf",&c[d]);
    if(c[0]==c[1]&&c[2]==c[3])printf("YES\n");
    else if(abs((c[1]-c[0])*(c[7]-c[6])==(c[3]-c[2])*(c[5]-c[4])))printf("YES\n");
    else printf("NO\n");
    }
}

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];
        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;
}

C++: #include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
int main(void) {
  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 ((y2 - y1) / (x2 - x1) == (y4 - y3) / (x4 - x3)) {
      cout << "YES";
    } else {
      cout << "NO";
    }
    cout << endl;
  }
  return 0;
}

C++: #include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <cfloat>
#include <ctime>
#include <cassert>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <numeric>
#include <list>
#include <iomanip>
  
using namespace std;
  
#if __GNUC__
#include <tr1/unordered_map>
#include <tr1/unordered_set>
using namespace tr1;
#else
#include <unordered_map>
#include <unordered_set>
#endif
  
  
  
#ifdef _MSC_VER
#define __typeof__ decltype
template <class T> int popcount(T n) { return n ? 1 + popcount(n & (n - 1)) : 0; }
#endif
#ifdef __GNUC__
template <class T> int popcount(T n);
template <> int popcount(unsigned int n) { return __builtin_popcount(n); }
template <> int popcount(int n) { return __builtin_popcount(n); }
template <> int popcount(unsigned long long n) { return __builtin_popcountll(n); }
template <> int popcount(long long n) { return __builtin_popcountll(n); }
#endif
  
#define rep (i, n) for (int i = 0; i < (int)n; ++i)
#define foreach(it, c) for (__typeof__((c).begin()) it=(c).begin(); it != (c).end(); ++it)
#define rforeach(it, c) for (__typeof__((c).rbegin()) it=(c).rbegin(); it != (c).rend(); ++it)
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define CL(arr, val) memset(arr, val, sizeof(arr))
#define MEMCPY(dest, src) memcpy(dest, src, sizeof(src))
  
  
template <class T> void max_swap(T& a, const T& b) { a = max(a, b); }
template <class T> void min_swap(T& a, const T& b) { a = min(a, b); }
  
typedef long long ll;
typedef pair<int, int> pint;
  
template <class T> string to_s(const T& a) { ostringstream os; os << a; return os.str(); }
  
const double EPS = 1e-8;
const double PI = acos(-1.0);
const int dx[] = { 0, 1, 0, -1 };
const int dy[] = { 1, 0, -1, 0 };
bool valid_pos(int x, int y, int w, int h) { return 0 <= x && x < w && 0 <= y && y < h; }
  
template <class T> void print(T a, int n, int br = 1, const string& deli = ", ") { cout << "{ "; for (int i = 0; i < n; ++i) { cout << a[i]; if (i + 1 != n) cout << deli; } cout << " }"; while (br--) cout << endl; }
template <class T> void print(const vector<T>& v, int br = 1, const string& deli = ", ") { print(v, v.size(), br, deli); }
template <class T> void print2d(T a, int w, int h, int width = -1, int br = 1) { for (int i = 0; i < h; ++i) { for (int j = 0; j < w; ++j) {    if (width != -1) cout.width(width); cout << a[i][j] << ' '; } cout << endl; } while (br--) cout << endl; }
  
template <class T> void input(int n, T& a) { for (int i = 0; i < n; ++i) cin >> a[i]; }
template <class T, class U> void input(int n, T& a, U& b) { for (int i = 0; i < n; ++i) cin >> a[i] >> b[i]; }
template <class T> vector<T> input(int n) { vector<T> res(n); for (int i = 0; i < n; ++i) cin >> res[i]; return res; }
 
 
 
const double EPS_FOR_LIB = 1e-9;
typedef double geo_type;
typedef complex<geo_type> Point;
typedef vector<Point> Poly;
namespace std
{
	bool operator<(const Point& a, const Point& b)
	{
		return a.real() != b.real() ? a.real() < b.real() : a.imag() < b.imag();
	}
	std::istream& operator>>(std::istream& is, Point& p)
	{
		geo_type a, b; is >> a >> b;
		p = Point(a, b);
		return is;
	}
	std::ostream& operator<<(std::ostream& os, Point& p)
	{
		return os << "(" << p.real() << ", " << p.imag() << ")";
	}
};
struct Line
{
	Point a, b;
	Line(Point a, Point b) : a(a), b(b) { }
	Line() { }
};

geo_type dot(const Point& a, const Point& b)
{
	return a.real() * b.real() + a.imag() * b.imag();
}
geo_type cross(const Point& a, const Point& b)
{
	return a.real() * b.imag() - a.imag() * b.real();
}

bool is_parallel(const Line& line1, const Line& line2)
{
	return abs(cross(line1.b - line1.a, line2.b - line2.a)) < EPS_FOR_LIB;
}

int main()
{
	int n;
	cin >> n;
	while (n--)
	{
		Point p[4];
		input(4, p);
		cout << (is_parallel(Line(p[0], p[1]), Line(p[2], p[3]))
			? "YES" : "NO") << endl;		
	}
}

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

int main() {
	int n;
	double x1, y1, x2, y2, x3, y3, x4, y4;
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		if (x2 - x1 == 0 || x4 - x3 == 0) {
			cout << "YES" << endl;
			continue;
		}
		double m1 = (y2 - y1) / (x2 - x1);
		double m2 = (y4 - y3) / (x4 - x3);
		if (m1 == m2) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	return 0;
}

C++: #include<iostream>
#include<cmath>
using namespace std;
struct point{
  double x,y;
    };
int main(){
  point p[4];
  int n;
  cin >> n;
  for(int i=0;i<n;i++){
    cin >> p[0].x >> p[0].y>>p[1].x>>p[1].y>>p[2].x>>p[2].y>>p[3].x>>p[3].y;
    if(fabs((p[1].y -p[0].y)*(p[3].x -p[2].x)- (p[3].y-p[2].y)*(p[1].x-p[0].x)) <1.0e-15){
	cout << "YES" << endl;
      } else {cout << "NO" << endl;}
      
  }
}

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

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

C++: #include<cmath>
#include<iostream>
int main(){int n;double E=1e-10,a,b,c,d,e,f,g,h;std::cin>>n;while(n--){std::cin>>a>>b>>c>>d>>e>>f>>g>>h;std::cout<<((fabs((d-b)*(g-e)-(h-f)*(c-a))<E)?"YES\n":"NO\n");}}