2Stack in one array

/*This Flie is Made by VISHESH YADAV (ECE-1) Netaji Subhas University Of technology*/


#include <stdio.h>
#define n 100

int top1=-1,top2=n,arr[n];

void push1(int val){
    if(top1<top2-1){
        arr[++top1]=val;
    }
    else{
        printf("Stack is full\n");
    }
}
 
void push2(int val){
    if(top1<top2-1){
        arr[--top2]=val;
    }
    else{
        printf("Stack is full\n");
    }
}

void pop1(){
 if(top1>=0){
    int popped_value= arr[top1--];
    printf("%d has been popped\n",popped_value); 
 }
 else{
    printf("Stack is empty\n");
 }
}

void pop2(){
    if(top2<n){
        int popped=arr[top2++];
        printf("%d element popped\n",popped);
    }
}

void display1(){
    int i;
    for(i=top1;i>=0;i--){
        printf("%d ",arr[i]);
    }
    printf("\n");
}

void display2(){
    int i;
    for(i=top2;i<n;i++){
        printf("%d ",arr[i]);
    }
    printf("\n");
}

int main(){
    int val,ch;
    while(1){
        printf("Enter choice\n1.Insert in stack1\n2.Insert in stack2\n3.pop in stack1\n4.pop in stack2\n5.display stack1\n6.display stack2\n");
        scanf("%d",&ch);
        switch(ch){
            case 1:{
                printf("Enter element to push: ");
                scanf("%d",&val);
                push1(val);
                break;
            }
            case 2:{
                printf("Enter element to push: ");
                scanf("%d",&val);
                push2(val);
                break;
            }
            case 3 : {
                pop1();
                break;
            }
            case 4:{
                pop2();
                break;
            }
            case 5:{
                display1();
                break;
            }
            case 6:{
                display2();
            }
            default:printf("Invalid!\n");
        }
    }
}