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<string>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int main(void){
    int n;
    double x1,x2,x3,x4,y1,y2,y3,y4;
    cin>>n;
    for(int i=0;i<n;i++){
        cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
 
 
    double a,b;
    a=(y2-y1)/(x2-x1);
    b=(y4-y3)/(x4-x3);
    (a==b)? cout<<"YES"<<endl : cout<<"NO"<<endl;
    }
    return 0;
}

C++: #include<cstdio>
#include<iostream>
#include<algorithm>
#include<vector>
#include<set>
#include<string>
#include<functional>
#include<queue>
#include<stack>
#include<math.h>
#define INF 999999
#define EPS 1.0e-6

using namespace std;

typedef long long ll;


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 a = (y2 - y1)*(x4 - x3) - (y4 - y3)*(x2 - x1);
		if (fabs(a) < EPS )printf("YES\n");
		else printf("NO\n");
	}
	
	return 0;
}

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

int main() {
    double n,x[4],y[4],judge1,judge2;
    cin >> n;
    for(int i=0;i<n;i++){
        for(int j=0;j<4;j++) cin>>x[j]>>y[j];
        judge1=(y[1]-y[0])/(x[1]-x[0]);
        judge2=(y[3]-y[2])/(x[3]-x[2]);
        if(judge1==judge2)cout << "YES";
        else cout << "NO";
        cout << endl;
    }
}

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

int main(){
	int n;cin >> n;
	float a[8], x1, x2, y1, y2, ans;
	while(n--){
		for(int i = 0;i < 8;i++)cin >> a[i];
		y1 = a[3]-a[1];x1 = a[2]-a[0];
		y2 = a[7]-a[5];x2 = a[6]-a[4];
		ans = y1*x2-y2*x1;
		if(ans == 0)cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	return 0; 
}

C++: #include <iostream>
#include <cmath>
#include <vector>
#include <string>
#include <algorithm>
#include <climits>
using namespace std;

int main(){
    double EPS = 1e-12;
    double x[4];
    double y[4];
    double s;
    double t;
    double u;
    double v;
    int n;
    cin >> n;

    for (int t = 0;t < n;++t) {
        for (int i = 0;i < 4;++i){
            cin >> x[i] >> y[i]; 
        }
    }
    s = x[1] - x[0];
    t = y[1] - y[0];
    u = x[3] - x[2];
    v = y[3] - y[2];

    if(s * v - t * u > 0){
        double m = s * v - t * u;
    }
    else{
        double m = t * u - s * v;
    }

    cout << "NO" << endl;
}

C++: #include<iostream>
#include<vector>
struct Coordinate {
	double x;
	double y;
};
std::vector<bool>l;
int main() {
	Coordinate A, B, C, D;
	double Inclination_of_AB;
	double Inclination_of_CD;
	int n;
	std::cin >> n;
	for (int i = 0; i < n; i++){
		std::cin >> A.x >> A.y >> B.x >> B.y;
		Inclination_of_AB = (B.x - A.x) / (B.y - A.y);
		std::cin >> C.x >> C.y >> D.x >> D.y;
		Inclination_of_CD = (D.x - C.x) / (D.y - C.y);
		if (Inclination_of_AB == Inclination_of_CD)
			l.push_back(true);
		else l.push_back(false);
	}
	for (bool i : l) {
		if (i)std::cout << "YES";
		else std::cout << "NO";
		std::cout << std::endl;
	}
	char c;
	std::cin >> c;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <sstream>
#include <utility>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;
#define all(c) (c).begin(), (c).end()
#define loop(i,a,b) for(ll i=a; i<ll(b); i++)
#define rep(i,b) loop(i,0,b)
#define each(e,c) for(auto&e:c)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
#define lb lower_bound
#define ub upper_bound
#ifdef DEBUG
#define dump(...) (cerr<<#__VA_ARGS__<<" = "<<(DUMP(),__VA_ARGS__).str()<<" ["<<__LINE__<<"]"<<endl)
struct DUMP:ostringstream{template<class T>DUMP &operator,(const T&t){if(this->tellp())*this<<", ";*this<<t;return *this;}};
#else
#define dump(...)
#endif

int main(){
    int n; cin>>n;
    rep(_,n){
        ll x[2][2], y[2][2];
        rep(i,2){
            rep(j,2){
                double x_,y_;
                cin >> x_ >> y_;
                x[i][j] = (x_ + 1e-6)*100000;
                y[i][j] = (y_ + 1e-6)*100000;
            }
        }
        ll dx1=x[0][0]-x[0][1], dy1=y[0][0]-y[0][1];
        ll dx2=x[1][0]-x[1][1], dy2=y[1][0]-y[1][1];
        dump(dx1,dx2,dy1,dy2);
        puts(dx1*dy2==dx2*dy1 ? "YES" : "NO");
    }
}

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

int main(){
	double x1,x2,x3,x4,y1,y2,y3,y4;
	int n;
	scanf("%d",&n);
	for(int i=0;i<n;i++){
			scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);
		if( (((y1-y2)==0 || (y3-y4)==0)&&(y1-y2)!=(y3-y4)) || ((x1-x2)==0 || ((x3-x4)==0)&&(x1-x2)!=(x3-x4))){
			
				printf("NO\n");
		}
			else if((y1-y2)*(x3-x4)==(x1-x2)*(y3-y4)){
				printf("YES\n");
			}
			else{
				printf("NO\n");
			}
		}
	
	return 0;
}

C++: #include<stdio.h>
#include<math.h>
 
int main(){
    float x1,x2,x3,x4,y1,y2,y3,y4;
    float a1=0.0,a2=0.0;
    int n,i;
     
    scanf("%d",&n);
     
    for(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");
    }
return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<string>
using namespace std;
int main() {
	int n;
	cin >> n;
	for (int z = 0; z < n; z++) {
		long float x1, x2, x3,y1, y2, y3, y4, x4 ;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		if (y1 > y2) {
			swap(y1, y2);
			swap(x1, x2);
		}
		if (y3 > y4) {
			swap(y3, y4);
			swap(x3, x4);
		}
		if ((x1 > x2&&x3 > x4 && ((y2 - y1) / (x1 - x2) == (y4 - y3) / (x3 - x4))) || (x2 > x1&&x4 > x3 && ((y1 - y2) / (x2 - x1) == (y3 - y4) / (x4 - x3)))) {
			cout << "YES" << endl;
		}
		else {
			cout << "NO" << endl;
		}
	}
}