C Program for implementing two Stacks on Single Array

#define SIZE 10            /* Size of Stack */
int s[SIZE],top[3]={0,-1,SIZE};
/* Global declarations */
push(int elem,int stno)
{
int pos;	     /* Function for PUSH operation */
if( Sfull()) printf("\n\n Overflow!!!!\n\n");
else
{
if(stno==1) pos= ++top[stno];
else pos=--top[stno];
s[pos]=elem;
}
}
 
int pop(int stno)
{                      /* Function for POP operation */
int elem,pos;
if(Sempty(stno)){ printf("\n\nUnderflow!!!!\n\n");
return(-1); }
else
{
pos=top[stno];
elem=s[pos];
if(stno == 1)top[stno]--;
else
top[stno]++;
return(elem);
}
}
 
int Sfull()
{                     /* Function to Check Stack Full */
if(top[1] == top[2]-1) return 1;
return 0;
}
 
int Sempty(stno)
{
/* Function to Check Stack Empty */
switch(stno)
{
case 1: if(top[1] == -1) return 1; else return 0;
case 2: if(top[2] == SIZE) return 1;else return 0;
}
}
 
display(int stno)
{                  /* Function to display status of Stack */
int i;
if(Sempty(stno)) printf(" \n Empty Stack\n");
else
{
if(stno == 1)
{
for(i=0;i<=top[stno];i++)
printf("%d\n",s[i]);
printf("^Top");
}
else
{
for(i=SIZE-1;i>=top[stno];i--)
printf("%d\n",s[i]);
printf("^Top");
}
}
}
 
main()
{                         /* Main Program */
int opn,elem,stno;
do
{
clrscr();
printf("\n ### Stack Operations ### \n\n");
printf("\n Stack Number (1,2): ");
scanf("%d",&stno);
printf("\n Press 1-Push, 2-Pop,3-Display,4-Exit\n");
printf("\n Your option ? ");
scanf("%d",&opn);
 
switch(opn)
{
case 1: printf("\n\nRead the element to be pushed ?");
scanf("%d",&elem);
push(elem,stno); break;
case 2: elem=pop(stno);
if( elem != -1)
printf("\n\nPopped Element is %d \n",elem);
break;
case 3: printf("\n\nStatus of Stack %d \n\n",stno);
display(stno); break;
case 4: printf("\n\n Terminating \n\n"); break;
default: printf("\n\nInvalid Option !!! Try Again !! \n\n");
break;
}
printf("\n\n\n\n  Press a Key to Continue . . . ");
getch();
}while(opn != 4);
}