C program to implement multiple stacks

#include <stdio.h>
#include <conio.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]);
}
}
void main()
{
int option, val;
clrscr();
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();
}