Зачем нужны конструктор и деструктор класса?

#include "stdafx.h"
#include <stdio.h>
#include <windows.h>
#include <iostream>
#include <conio.h>
#include <math.h>
#include "class.h"
 
class X
{
        double *x,*y,*z,res;
        friend void run();
        friend void print();
public:
    X(double=0, double=0, double=0);
    ~X();
};
 
X :: X(double x1, double y1, double z1)
    {//конструктор
        x=new double;
            x1=*x;
        y=new double;
            y1=*y;
        z=new double;
            z1=*z;
    }
 
void run(){
    res=(pow(y,x+1))/(pow(fabs(y-2),1.0/3)+3)+(x+y/2)/(2*fabs(x+y))*pow(x+1,(-1/sin(z)));
}
 
void print()
{
    std::cout<<"\nResult:"<<res;
}
 
X:: ~X() {};//деструктор
 
void main(void)
{
X(1.23,15.4,252.0);
run();
print();
getch();
}

res=(pow(y,x+1))/(pow(fabs(y-2),1.0/3)+3)+(x+y/2)/(2*fabs(x+y))*pow(x+1,(-1/sin(z)));

#include <iostream>
using std::cin;
using std::cout;
using std::endl;
 
#include <cmath>
 
class X {
private:
    double *x;
    double *y;
    double *z;
public:
    X(double x1, double y1, double z1);
    ~X();
    friend void printX(X obj);
    friend void runX(X obj);
};
 
X::X(double x1=0, double y1=0, double z1=0){
    x = new double(x1);
    y = new double(y1);
    z = new double(z1);
}
 
X::~X(){
    delete x;
    delete y;
    delete z;
}
 
void printX(X obj){
    cout << *(obj.x) << '\t' << *(obj.y) << '\t' << *(obj.z) << endl;
}
 
void runX(X obj){
    double x,y,z,res;
    x = *(obj.x);
    y = *(obj.y);
    z = *(obj.z);
    res=(pow(y,x+1.0))/(pow(fabs(y-2.0),1.0/3.0+3.0))+(x+y/2.0)/(2.0*fabs(x+y))*pow(x+1.0,(-1.0/sin(z)));
    cout << res << endl;
}
 
 
int main( void ){
    double a, b, c;
    cout << "Enter three double values for X: ";
    cin >> a >> b >> c;
    X o(a,b,c);
    cout << "Print X values:" << endl;
    printX(o);
    cout << "Calculate X values:" << endl;
    runX(o);
    return 0;
}

X:: ~X() {;delete x; delete y; delete z;};

run (X& ob);