multiple stack

#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#define MAX 10
int stack[MAX],topA=-1,topB=MAX;
void pushA(int val)
 {
  if(topA==topB-1)  
  printf("\n OVERFLOW");
   else
    {
	  topA+= 1;
	   stack[topA] = val; 
	   }
	    } 
int popA() 
{
 int val; 
 if(topA==-1)
  { 
   printf("\n UNDERFLOW");  
   val = -999; 
   } 
   else
    { 
	 val = stack[topA];  
	 topA--; 
	 } 
	 return val;
	  } 
	  void display_stackA() 
	  {
	   int i;
	    if(topA==-1)  
		printf("\n Stack A is Empty");
		 else 
		 {  
		 for(i=topA;i>=0;i--) 
		   printf("\t %d",stack[i]); 
		   } 
		   }
		    void pushB(int val)
			 {
			  if(topB-1==topA)
			    printf("\n OVERFLOW");
				 else
 {  
 topB -= 1;
   stack[topB] = val;
    }
	 } 
	 int popB() 
	 { 
	 int val;
	  if(topB==MAX)
	   { 
	    printf("\n UNDERFLOW"); 
		 val = -999;
		  } 
		  else
		   {  
		   val = stack[topB];  
		   topB++;
		    }
			 }
 void display_stackB() 
 {
  int i;
   if(topB==MAX)
     printf("\n Stack B is Empty");
	  else 
	  { 
	   for(i=topB;i<MAX;i++)  
	    printf("\t %d",stack[i]);
		 }
		  } 
		  int main()
		   { 
		   int option, val; 
			do {  
			printf("\n *****MENU*****");  
			 printf("\n 1. PUSH IN STACK A");
			   printf("\n 2. PUSH IN STACK B");  
			   printf("\n 3. POP FROM STACK A");
			     printf("\n 4. POP FROM STACK B");
				   printf("\n 5. DISPLAY STACK A"); 
				    printf("\n 6. DISPLAY STACK B");  
					printf("\n 7. EXIT");
					  printf("\n Enter your choice"); 
					   scanf("%d",&option); 
					    switch(option) 
						 { 
						   case 1: printf("\n Enter the value to push on Stack A : ");   
						    scanf("%d",&val); 
							pushA(val); 
							break; 
							  case 2: printf("\n Enter the value to push on Stack B : "); 
							     scanf("%d",&val);  
								   pushB(val); 
								      break; 
									    case 3: val=popA(); 
										   if(val!=-999)  
										       printf("\n The value popped from Stack A = %d",val);  
											     break;
   case 4: val=popB();  
     if(val!=-999)
	       printf("\n The value popped from Stack B = %d",val); 
		      break; 
			    case 5: printf("\n The contents of Stack A are : \n"); 
				   display_stackA();  
				     break;  
					  case 6: printf("\n The contents of Stack B are : \n"); 
					     display_stackB();   
						  break;
						    } 
							}
							while(option!=7); 
							getch();
							 }