Factorial using stack cpp program

CPP program to implement factorial of a number using stack.

#include<iostream.h>

#include<conio.h>

#include<math.h>

#include<stdlib.h>

class stack

{private:

          int top;

          int para_n[100];

 public:

          void push(stack *,int);

          void pop(stack *,int* );

          double fact(int);

}s;

void stack::push(stack *s,int d)

{        s->top++;

          s->para_n[s->top]=d;

}

void stack::pop(stack *s,int *d)

{        *d=s->para_n[s->top];

          s->top--;

}

double stack::fact(int n)

{        double res;

          int d;

          d=n;

          s.top=-1;

          lab1:

                    if(d==0)

                   {        res=1;

                             goto lab2;

                   }

                    else

                   {        push(&s,d);

                             d--;

                             goto lab1;

                   }

          lab2:

                    if(s.top>-1)

                   {        pop(&s,&d);

                             res*=d;

                             goto lab2;

                   }

                   else

                             return res;

}

void main()

{        int num,c;

          stack k;

          clrscr();

          while(1)

          {        clrscr();

                   do{

                   clrscr();

                   cout<<"\nTo Find the factorial of a number\n\n";

                   cout<<"------------------------------------------\n";

                   cout<<"1.Enter a number";

                   cout<<"\n2.Display factorial";

                   cout<<"\n3.Exit from the program";

                   cout<<"\n\nSelect yourchoice _ ";

                   cin>>c;

                   }while((c<1)||(c>3));

          if(c==3)exit(1);

          switch(c)

          {case 1 :

                   clrscr();

                   cout<<"\nEnter your number ";

                    cin>>num;

                    break;

          case 2 :

                   clrscr();

                   cout<<num<<"!="<<k.fact(num);

                   break;

          }

          cout<<"\n\nPress any key to continue...........";

 getch();

    }

}