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>
using namespace std;

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

C++: #include<iostream>

int main(){
  int n;
  double x1,y1,x2,y2,x3,y3,x4,y4;
  const double e = 1e-12;

  std::cin >> n;

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

    if((x1*y3+x2*y4+y2*x3+y1*x4)-(x2*y3+x1*y4+y1*x3+y2*x4)<e){
      std::cout << "YES" << std::endl;
    }else{
      std::cout << "NO" << std::endl;
    }
  }
}

C++: #include <functional>
#include <algorithm>
#include <iostream>
#include <numeric>
#include <iomanip>
#include <utility>
#include <cstdlib>
#include <sstream>
#include <bitset>
#include <vector>
#include <cstdio>
#include <ctime>
#include <queue>
#include <deque>
#include <cmath>
#include <stack>
#include <list>
#include <map>
#include <set>

using namespace std;


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

const double EPS = 1e-11;
const double INF = 100000000;




int main(){
    int n;
    cin>>n;
    rep(i,n){
        double x[4],y[4],ax,ay,bx,by,ans;
        
        rep(j,4){
            cin>>x[j]>>y[j];
        }
        
        ax=x[1]-x[0];
        ay=y[1]-y[0];
        bx=x[3]-x[2];
        by=y[3]-y[2];
        
        ans=ax*by-bx*ay;
        if(fabs(ans)<=EPS)cout<<"YES"<<endl;
        else cout<<"NO"<<endl;
        
    }
    
    return 0;
}

C++: 
#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
#include <cfloat>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <iostream>
#include <memory>
#include <string>

#include <algorithm>
#include <complex>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <vector>

using namespace std;

#ifdef _MSC_VER
#define __typeof__ decltype
#endif

#define ITER(c)         __typeof__((c).begin())
#define FOREACH(it, c)  for (ITER(c) it=(c).begin(); it != (c).end(); ++it)
#define RITER(c)        __typeof__((c).rbegin())
#define RFOREACH(it, c) for (RITER(c) it=(c).rbegin(); it != (c).rend(); ++it)
#define REP(i, n)       REPEAT(i, 0, n)
#define REPEAT(i, k, n) for (int i = (k); i < (n); ++i)
#define REVREP(i, n)    for (int i = ((n)-1); i >= 0; --i)
#define FIND(c, n)      std::find((c).begin(), (c).end(), (n));
#define BSEARCH(c, n)   std::binary_search((c).begin(), (c).end(), (n))
#define LLPOW(p1,p2)    ((ll)pow((double)(p1), (int)p2))
#define ESIZEOF(A)      (sizeof(A)/sizeof((A)[0]))
#define MIN(p1,p2)      (((p1)<(p2))?(p1):(p2))
#define MAX(p1,p2)      (((p1)>(p2))?(p1):(p2))
#define CIN_NO_SYNC     do { cin.tie(0); ios_base::sync_with_stdio(false); } while(0)
#define GETSTR(p)       fgets((p), sizeof(p), stdin)
#define CHOMP(p)        do{ char *_q = (p) + strlen(p)-1; if(*_q == '\n') *_q = 0; } while(0)

#define X real()
#define Y imag()
typedef double D;
typedef complex<double>P;
#define EPS (1e-9)

bool iscross(P &p1, P &p2, P &p3, P &p4){
    P d1 = p2 - p1, d2 = p4 - p3;
    D det = d2.X * d1.Y - d1.X * d2.Y;
    if(abs(det) < EPS) return false;
    return true;
}

int main(){
    int n;
    cin >> n;
    REP(i,n){
        double x1, y1, x2, y2, x3, y3, x4, y4;
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
        P p1(x1,y1), p2(x2,y2), p3(x3,y3), p4(x4,y4);
        if(!iscross(p1,p2,p3,p4)){
            cout << "YES" << endl;
        } else {
            cout << "NO" << endl;
        }
    }
    return 0;
}

C++: #include<iostream>
#include<cmath>
using namespace std;
int main(){
  double a[2],b[2],c[2],d[2];
  int n;
  cin >> n;
  for(int i=0;i<n;i++){
    for(int j=0;j<2;j++) cin >> a[j] >> b[j] >> c[j] >> d[j];
    if(a[0]-b[0]==0&&c[0]-d[0]==0) cout << "YES" << endl;
    else if(a[1]-b[1]==0&&c[1]-d[1]==0) cout << "YES" << endl;
    else if(fabs(a[0]*d[0]+a[1]*d[1])==fabs(b[0]*c[0]+b[1]*c[1])) cout << "YES" << endl;
    else cout << "NO" << endl;
  }   
  return 0;
}