Go: package main

import (
        "fmt"
        "math/big"
)

func main() {
        var x1, x2, x3, x4, y1, y2, y3, y4 big.Float
        var n int
        fmt.Scanf("%d", &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)
                var lx, ly, mx, my, mul1, mul2, sub, zz big.Float
                lx.Sub(&x2, &x1)
                ly.Sub(&y2, &y1)
                mx.Sub(&x4, &x3)
                my.Sub(&y4, &y3)
                mul1.Mul(&lx, &my)
                mul2.Mul(&ly, &mx)
                sub.Sub(&mul1, &mul2)
                zz.SetFloat64(0.0)

                if sub.Cmp(&zz) == 0 {
                        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-13;
// 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 = x1 - x2, t = y1 - y2, u = x3 - x4, v = y3 - y4;
		 if (s * v - t * u < EPS) {
			 PRINT("YES");
		 } else {
			 PRINT("NO");
		 }
	}

	return 0;
}

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

C++: #include<cstdio>
#include<cstdlib>
#include<cmath>
 
using namespace std;
int main(void)
{
    int n;
    double x[4],y[4];
    double k[2];
    scanf("%d",&n);
    for(int i = 0;i < n;i++)
    {
        for(int j = 0;j < 4;j++) scanf("%lf%lf",&x[j],&y[j]);
        k[0] = (y[0]-y[1])/(x[0]-x[1]);
        k[1] = (y[2]-y[3])/(x[2]-x[3]);
        if(k[0] == k[1]) printf("YES\n");
        else printf("NO\n");
    }
    return 0;
}

C++: #include <cmath>
#include <iostream>
#include <string>
#include <cstdlib>
#include <cstdio>
#include <algorithm>
#include <sstream>

using namespace std;

typedef struct{
    double x;
    double y;
}vec;

int main(){
    int n;
    vec p[4];
    cin >> n;
    while(n--){
        for(int i=0;i<4;i++)
            cin >> p[i].x >> p[i].y;
        p[0].x-=p[1].x;
        p[0].y-=p[1].y;
        p[2].x-=p[3].x;
        p[2].y-=p[3].y;
        if(p[0].x*p[2].y-p[0].y*p[2].x==0) cout << "YES" << endl;
        else cout << "NO" << endl;
    }
    return 0;
}

C++: #include <cstdio>
#include <cstring>
#include <string>
#include <cmath>
#include <cassert>
#include <iostream>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
#include <set>
#include <map>
#include <bitset>
#include <functional>
#include <sstream>
#include <utility>
#include <cstdlib>
#include <cctype>
#include <climits>
#include <fstream>

using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<double> vd;
typedef vector<pair<int, int> > vpii;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n) for(int i=0;i<(n);++i)
#define foreach(itr,c) for(__typeof(c.begin()) itr=c.begin(); itr!=c.end(); itr++)
#define dbg(x) cout << #x"="<< (x) << endl
#define mp(a,b) make_pair((a),(b))
#define pb(a) push_back(a) 
#define in(x) cin >> x;
#define all(x) (x).begin(), (x).end()
#define INF 2147483600
#define fi first
#define se second
using namespace std;
const double eps = 1e-10;//????????????????????????

int main(){
	int N;
	vd a(8);
	cin >> N;
	rep(i,N){
		rep(i,8){
			cin>>a[i];
		}
		if(abs((a[1]-a[3])*(a[4]-a[6])-(a[5]-a[7])*(a[0]-a[2]))< eps){
			cout<<"YES"<<endl;
		}else{
			cout<<"NO"<<endl;
		}
	}

}

C++: #include <stdio.h>

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

C++: #include <iostream>
#include <cmath>

using namespace std;

int main() {
    int n;
    cin >> n;
    while (n--) {
        double x1, x2, x3, x4, y1, y2, y3, y4;
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
        if (abs((x4 - x3) * (y2 - y1) - (x2 - x1) * (y4 - y3)) < 1e-10) {
            cout << "YES" << endl;
        }
        else {
            cout << "NO" << endl;
        }
    }
    
    return 0;
}

C++: #include<cmath>
#include<iostream>
#include<algorithm>
#include<iomanip>
#include<vector>
#include<string>
#include<queue>
#include<stack>
#include<cstdio>
#include<map>
#define rep(i,n) for(int i=0;i<n;i++)
#define fori(i,k,n) for(int i=k;i<n;i++)
using namespace std;
const int dx[4] = { 0, 1, 0, -1 }, dy[4] = { 1, 0, -1, 0 };
const int dX[8] = { 0, 1, 1, 1, 0, -1, -1, -1 }, dY[8] = { 1, 1, 0, -1, -1, -1, 0, 1 };
/*
(char)'1' - (int)48 = (int)1; 


*/


int main()
{
	int n;
	cin >> n;
	while (n--){
		double x[4], y[4];
		rep(i, 4)cin >> x[i]>>y[i];
		rep(i, 4)
		{
			x[i] += 0.15125;
			y[i] +=0.15125;;

		}
		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++: #define scanf_s scanf
//#define gets_s gets
#include <stdio.h>
#include <string>
#include <iostream>
#include <math.h>
using namespace std;
#define MAX 201
#define _MAX 100
#define ABC 26
int main(void)
{
	int n;
	double x1, y1, x2, y2, x3, y3, x4, y4, a1, b1, a2, b2;
	scanf_s("%d", &n);
	for (int i = 0; i < n; ++i) {
		scanf_s("%lf %lf %lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3, &x4, &y4);
		a1 = (y2 - y1) / (x2 - x1);
		a2 = (y4 - y3) / (x4 - x3);
		//a1 = (y1 - y2) / (x1 - x2);
		//a2 = (y3 - y4) / (x3 - x4);
		if (a1 == a2)
			printf("YES\n");
		else
			printf("NO\n");
	}
}

C++: #include <stdio.h>
#include <iostream>

using namespace std;

int main() {
	int k;
	double x1,x2,x3,x4,y1,y2,y3,y4;
	double veku1[2];
	double veku2[2];
	double veku3[2];
	double t;
	double m;
	cin >> k;

	for (int i = 0; i < k; i++) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		veku1[0] = x2 - x1;
		veku1[1] = y2 - y1;
		veku2[0] = x4 - x3;
		veku2[1] = y4 - y3;

		t = veku1[0] * veku2[0] + veku1[1] * veku2[1];

		if (t * t != (veku1[0] * veku1[0] + veku1[1] * veku1[1]) * (veku2[0] * veku2[0] + veku2[1] * veku2[1])) {
			cout << "NO" << endl;
		} else {
			veku3[0] = x3 - x1;
			veku3[1] = y3 - y1;
			m = veku1[0] * veku3[0] + veku1[1] * veku3[1];
			if (m * m != (veku1[0] * veku1[0] + veku1[1] * veku1[1]) * (veku3[0] * veku3[0] + veku3[1] * veku3[1])) {
				cout << "YES" << endl;
			} else {
				cout << "NO" << endl;
			}
		}
	}
	return 0;
}

C++: #include <iostream>
#include <math.h>

using namespace std;

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

	cin >> n;

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

		dega = (y2 - y1) / (x2 - x1);
		degb = (y4 - y3) / (x4 - x3);
	
		if(dega == degb){
			cout << "YES" << endl;
		}else{
			cout << "NO" << endl;
		}
	}

	return 0;
}