pilha par

#include <stdio.h>
#include <stdlib.h>
#define max 20

struct stack{

    int vet[max];
    int top;

    }typedef node;

void iniciar(node *p) {
    p->top=-1;
}

void push(node *p,int x){

    if (p->top==19) printf("%s","\nStack Overflow\n");
    else{
    p->top++;
    p->vet[p->top]=x;
    }

    }


int pop(node *p){

    int x;

    if(p->top==-1)printf("%s","\nStack Underflow\n");

    x=p->vet[p->top];
    p->top--;

    return x;

    }


void mostrar(node *p){

    int i;
    if(p->top==-1)printf("%s","\nStack Underflow\n");
    printf("\n");
    for(i=p->top;i>=0;i--) printf("[%d]\n",p->vet[i]);

    }

void menor100(node *p){

    printf("%d\n",p->vet[p->top]);

    }

int menu(){

    int opc;

    printf(" _________________________________\n");
    printf("|_______________Menu______________|\n");
    printf("|                                 |\n");
    printf("|0-Sair                           |\n");
    printf("|1-Inserir                        |\n");
    printf("|2-Excluir.                       |\n");
    printf("|3-Mostrar.                       |\n");
    printf("|4-Topo                           |\n");
    printf("|_________________________________|\n");

    printf("Digite uma opcao: ");
    scanf("%d",&opc);

    return opc;

    }


int main(){

   int x,opc;
   node pilha;
   iniciar(&pilha);

   do{

       opc=menu();

       switch(opc){

           case 0:



                 break;

           case 1:

                 printf("Digite um valor: ");
                 scanf("%d",&x);
                 push(&pilha,x);


                 break;

           case 2:

                 printf("Excluido: %d\n",pop(&pilha));

                 break;

           case 3:

                mostrar(&pilha);

                 break;

           case 4:

                menor100(&pilha);

                 break;

           default:

                  printf("Opcao invalida\n");

                  break;


           }

           system("pause");
           system("cls");

       }while(opc!=2);



return 0;
}