Multiple stack

#include <stdio.h>
#include <malloc.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 a element into Stack A");
printf("\n 2. PUSH a element into Stack B");
printf("\n 3. POP a element from Stack A");
printf("\n 4. POP a element from Stack B");
printf("\n 5. Display the Stack A");
printf("\n 6. Display the 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:
if(val != -999)
printf("\n The value popped from Stack A = %d", val);
break;
case 4:
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);
return 0;
}