Push Pop

#include<stdio.h> #include<conio.h> #define MAX 100 struct stack {   int item[MAX];   int tos; }; typedef struct stack st; void push(st*, int); int pop(st*); void display(st*); void main() {    int dta, ch, x;    st *s;    clrscr();    s->tos=-1;    printf("\n**************menu for program*************:\n");    printf("1:push\n2:pop\n3:display\n4:exit\n");    do    { printf("\nEnter yout choice\n"); scanf("%d",&ch); switch(ch) {   case 1:   printf("Enter data to be inserted\n");   scanf("%d",&dta);   push(s,dta);   break;   case 2:   x=pop(s);   printf("\npoped item is:");   printf("%d\n",x);   break;   case 3:   display(s);   break;   default:   exit(1); }   }while(ch<4);    getch(); } /*******push function**************/ void push(st *s,int d) { if(s->tos==MAX-1) {   printf("Stack is full\n"); } else {    ++s->tos;    s->item[s->tos]=d; } } /***********pop function**************/ int pop(st *s) {   int itm;   if(s->tos==-1)   {      printf("Stack is empty\n");      return(0);   }   else   {   itm=s->item[s->tos];   s->tos--;   return(itm);   } } /*************display function********************/  void display(st *s)  { int i;     if(s->tos==-1)     printf("There is no data item to display\n");     else     { for(i=s->tos; i>=0; i--) {   printf("%d\t", s->item[i]); }     }  }