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 <cstdio>
#include <queue>
#include <algorithm>
#include <cmath>

#define rep(i, n) for(int i = 0; i < (n); ++i)

using namespace std;

int n;
double x[4];
double y[4];

int main(){
	scanf("%d", &n);
	rep(i, n){
		rep(j, 4){
			scanf("%lf%lf", x + j, y + j);
		}

		double dx[2];
		double dy[2];
		dx[0] = x[0] - x[1];
		dx[1] = x[2] - x[3];
		dy[0] = y[0] - y[1];
		dy[1] = y[2] - y[3];

		// printf("(%lf, %lf) (%lf, %lf)\n", dx[0], dy[0], dx[1], dy[1]);

		printf("%s\n", dx[0] * dy[1] == dx[1] * dy[0] ? "YES" : "NO");
	}
	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;

int main(){
    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 <iostream>

using namespace std;

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

C++: #include <stdio.h>

int main(void)
{
  int n,i;
  double x1,y1,x2,y2,x3,y3,x4,y4;
  int ans[100];
  
  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);
  
    x2 -= x1;
    y2 -= y1;
    x4 -= x3;
    y4 -= y3;

    if(x2 == 0 || x4 == 0){
      if(x2 == 0 && x4 == 0){
	ans[i] = 1;
      }else{
	ans[i] = 0;
      }
    }else{
      if(y2/x2 == y4/x4){
	ans[i] = 1;
      }else{
	ans[i] = 0;
      }
    }
  }
  for(i = 0;i < n;i++){
    if(ans[i] == 1){
      printf("YES\n");
    }else{
      printf("NO\n");
    }
  }   
  return 0;
}

C++: #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 <ctime>
#include <cstring>

#define ll long long
#define ull unsigned long long
#define pii pair<int,int>
#define vi vector<int>
#define VS vector<string>
#define all(x) x.begin(),x.end()
#define mp make_pair
#define pb push_back

using namespace std;

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

C++: #include <iostream>
#include <sstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <climits>
#include <cfloat>
using namespace std;

int main()
{
    int n;
    cin >> n;
    while(n-- > 0){
        vector<double> x(4), y(4);
        for(int i=0; i<4; ++i)
            cin >> x[i] >> y[i];
        if(fabs((y[1]-y[0]) * (x[3]-x[2]) - (y[3]-y[2]) * (x[1]-x[0])) < 1.0e-5)
            cout << "YES" << endl;
        else
            cout << "NO" << endl;
    }
    return 0;
}

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

using namespace std;

#define LOG(...) printf(__VA_ARGS__)
//#define LOG(...)
#define FOR(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define RSORT(c) sort((c).rbegin(),(c).rend())
#define CLR(a) memset((a), 0 ,sizeof(a))

typedef long long ll;
typedef unsigned long long ull;
typedef vector<bool> vb;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vb> vvb;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int dx[] = { -1, 0, 1, 0 }; const int dy[] = { 0, 1, 0, -1 };

int main() {
	int n;
	cin>>n;
	while (n--){
		vector<pair<double, double>> pos(4);
		REP(i, 4){
			cin >> pos[i].first >> pos[i].second;
		}

		if (abs((pos[1].first - pos[0].first)*(pos[3].second - pos[2].second) - (pos[1].second - pos[0].second)*(pos[3].first - pos[2].first))<=0.0001)
			cout << "YES"<<endl;
		else
			cout << "NO"<<endl;
		
	}
}

C++: #include <bits/stdc++.h>

using namespace std;

typedef complex<double> P;

#define EPS (1e-7)

double cross(P const& a, P const& b) {
  return imag(conj(a)*b);
}

bool is_parallel(P const& a1, P const& a2, P const& b1, P const& b2)
{ return abs(cross(a2-a1, b2-b1)) <= EPS; }

int main() {
  
  int N; cin >> N;
  for(int i=0; i<N; i++) {
    P ps[4];
    for(int i=0; i<4; i++)
      cin >> ps[i].real() >> ps[i].imag();
    printf("%s\n", (is_parallel(ps[0], ps[1], ps[2], ps[3]) ? "YES" : "NO" ));
  }
  
  return 0;
}

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

using namespace std;

typedef complex<double> Point;

bool parallel(const Point &v1, const Point &v2) {
    return abs(v1.real()*v2.imag() - v1.imag()*v2.real()) < 1e-6;
}

int main() {
    int N;
    cin >> N;
    while(N--) {
        Point ps[4];
        for(int i = 0; i < 4; ++i) cin >> ps[i].real() >> ps[i].imag();
        Point v1 = ps[1]-ps[0], v2 = ps[3]-ps[2];

        if(parallel(v1, v2)) cout << "YES" << endl;
        else cout << "NO" << endl;
    }
    return 0;
}