Language: C++

#include <vector>
#include <algorithm>
#include <iostream>
#include <cstdio>
#include <cmath>
#include <climits>

using namespace std;

#define EPS (1e-10)
#define equals(a, b) (fabs((a) - (b)) < EPS)

//???
class Point {
public:
    double x, y;
    
    Point (double x = 0, double y = 0):x(x), y(y){}
    Point operator + (Point p){return Point(x + p.x, y + p.y);}
    Point operator - (Point p){return Point(x - p.x, y - p.y);}
    Point operator * (double a){return Point(a * x, a * y);}
    Point operator / (double a){return Point(x / a, y / a);}
    
    double norm(){return x*x + y*y;};
    double absolute(){return sqrt(norm());};
    
    bool operator < (const Point &p) const{
        return x != p.x ? x < p.x : y < p.y;
    }
    
    bool operator == (const Point &p) const{
        return equals(x, p.x) && equals(y, p.y);
    }
    
};
typedef Point Vector;                               //????????????
typedef struct Segment{Point p1, p2;}Segment;       //??????
typedef Segment Line;                               //??´???

//????????????a,b?????????
double dot(Vector a, Vector b){
    return a.x * b.x + a.y * b.y;
}
//????????????a,b?????????
double cross(Vector a, Vector b){
    return a.x * b.y - a.y * b.x;
}
//??´???s??¨???p????????¢
double getDistanceLP(Line l, Point p){
    return abs(cross(l.p2 - l.p1, p - l.p1) / absolute(l.p2 - l.p1));
}

//??????s(p1p2)??¨???p????????¢d????±???????
//??\???????????????????????§??´?????????
//??????????????????p2-p1??¨???????????????p-p1??????????§???????90???????????§????????´???????????????-90?????????????°?????????´?????????d??????p??¨???p1??¨????????¢
//??????????????????p1-p2??¨???????????????p-p2??????????§???????90???????????§????????´???????????????-90?????????????°?????????´?????????d??????p??¨???p2??¨????????¢
//??????????????\???????????????????????´??????d??????p??¨??´???p1p2????????¢
double getDistanceSP(Segment s, Point p){
    if (dot(s.p2 - s.p1, p - s.p1) < 0.0) return absolute(p - s.p1);
    if (dot(s.p1 - s.p2, p - s.p2) < 0.0) return absolute(p - s.p2);
    return getDistanceLP(s, p);
}


//??????p0, p1, p2???????????????????????????p0p1???????????????p2??????????????????
static const int COUNTER_CLOCKWISE = 1;
static const int CLOCKWISE = -1;
static const int ONLINE_BACK = 2;
static const int ONLINE_FRONT = -2;
static const int ON_SEGMENT = 0;
int ccw(Point p0, Point p1, Point p2){
    Vector a = p1 - p0;
    Vector b = p2 - p0;
    if(cross(a, b) > EPS) return COUNTER_CLOCKWISE;
    if(cross(a, b) < -EPS) return CLOCKWISE;
    if(dot(a, b) < -EPS) return ONLINE_BACK;
    if(norm(a) < norm(b)) return ONLINE_FRONT;
    return ON_SEGMENT;
}

//??????S1(p1p2)??¨??????s2(p2p3)????????????????????????
bool intersect(Point p1, Point p2, Point p3, Point p4){
    return  ccw(p1, p2, p3) * ccw(p1, p2, p4) <= 0
            &&
            ccw(p3, p4, p1) * ccw(p3, p4, p2) <= 0;
}
bool intersect(Segment s1, Segment s2){
    return intersect(s1.p1, s1.p2, s2.p1, s2.p2);
}

//??????s1??¨??????s2????????¢
//??\????????????????????¢????????§????????????????????????
//????????????s1??¨??????s2????§????s2.p1????????¢
//????????????s1??¨??????s2?????????s2.p2????????¢
//????????????s2??¨??????s1????§????s1.p1????????¢
//????????????s2??¨??????s1?????????s1.p2????????¢
double getDistance(Segment s1, Segment s2){
    if ( intersect(s1, s2) ) return 0.0;
    return min(
               min(getDistanceSP(s1, s2.p1), getDistanceSP(s1, s2.p2)),
               min(getDistanceSP(s2, s1.p1), getDistanceSP(s2, s1.p2))
               );
}

int main(){
    
    int x0, y0, x1, y1, x2, y2, x3, y3;
    
    int q;
    
    cin >> q;
    
    for (int i = 0; i < q; i++) {
        cin >> x0 >> y0 >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
        
        Point p0 = Point(x0, y0);
        Point p1 = Point(x1, y1);
        Point p2 = Point(x2, y2);
        Point p3 = Point(x3, y3);
        
        Segment s1 = {p0, p1};
        Segment s2 = {p2, p3};
        
        double ans = getDistance(s1, s2);
        
        printf("%.8lf\n", ans);
    }

    return 0;
}

Compiler output:
a.cc: In function 'double getDistanceLP(Line, Point)':
a.cc:50:47: error: 'absolute' was not declared in this scope
   50 |     return abs(cross(l.p2 - l.p1, p - l.p1) / absolute(l.p2 - l.p1));
      |                                               ^~~~~~~~
a.cc: In function 'double getDistanceSP(Segment, Point)':
a.cc:59:50: error: 'absolute' was not declared in this scope
   59 |     if (dot(s.p2 - s.p1, p - s.p1) < 0.0) return absolute(p - s.p1);
      |                                                  ^~~~~~~~
a.cc:60:50: error: 'absolute' was not declared in this scope
   60 |     if (dot(s.p1 - s.p2, p - s.p2) < 0.0) return absolute(p - s.p2);
      |                                                  ^~~~~~~~
a.cc: In function 'int ccw(Point, Point, Point)':
a.cc:77:8: error: 'norm' was not declared in this scope
   77 |     if(norm(a) < norm(b)) return ONLINE_FRONT;
      |        ^~~~