Complete stack program using switch case:

#include<stdio.h>
#include<conio.h>
#define max_size 40
typedef struct stack
{
        int element[max_size];
        int tos;
        }stack;
       
        void init_stack(stack *);
        void push(stack *,int item);
        int pop(stack *);
        void display(stack *);
       
        int main()
        {
            stack s;
            int i;
            int ch;
            init_stack(&s);
            push(&s,1);
            push(&s,2);
            push(&s,3);
            push(&s,4);
            push(&s,5);
           
            while(ch!=4)
            {
                   printf("\n press 1 to push \n");
                   printf("press 2 to pop \n");
                   printf("press 3 to display \n");
                   printf("press 4 to quit \n");
                   printf("enter your choice: \n");
                   scanf("%d",&ch);
                   switch(ch)
                   {
                       case 1:
                       printf("\n enter the element to be pushed \n");
                       scanf("%d",&i);
                       push(&s,i);
                       break;
                      
                       case 2:
                       i=pop(&s);
                       printf("\n you have popped value %d \n",i);
                       break;
                      
                       case 3:
                       display(&s);
                       break;
                      
                       case 4:
                       break;
                      
                       default:
                       printf("\n wrong choice try again \n");
                      }
                  }
                 getch();
                }
                                                         
                void init_stack(stack *s)
                {
                      s->tos=-1;
                }
                                                              
                void push(stack *s,int item)
                {
                     if(s->tos==max_size-1)
                     printf("overflow situation \n");
                     else
                     {
                           s->tos=s->tos+1;
                           s->element[s->tos]=item;
                      }
                 }
                                                                       
                int pop(stack *s)
                 {
                      int data;
                      if(s->tos==-1)
                      {
                          printf("underflow situation \n");
                          return NULL;
                       }
                       else
                       {
                           data=s->element[s->tos];
                           s->tos=s->tos-1;
                           return(data);
                        }
                  }
                                                                                             
                  void display(stack *s)
                  {
                      int i;
                      if(s->tos==-1)
                      printf("stack is empty, nothing to display \n");
                      else
                       {
                           for(i=s->tos;i>=0;i--)
                           printf("%d ",s->element[i]);
                      }
                   }