Pila Dinamica C

// Bibliotecas
#include
#include
#include
//-------------------------------------------------------------------------------------------------------------------------------------
//Estructuras
struct PILA{
int dato;
struct PILA *sig;
};
typedef struct PILA pila;
typedef pila *pilaptr;//-------------------------------------------------------------------------------------------------------------------------------------
// Prototipo de funciones
void menu();
void imprime(pilaptr actual);
void push(pilaptr *tope, int intro);
int pop(pilaptr *tope);int validar(pilaptr actual);
//-------------------------------------------------------------------------------------------------------------------------------------
int main(){
pilaptr stack =NULL;
int valor, opc;
menu();
scanf("%d", &opc);
while(opc!=4){
switch( opc ){
case 1:
system("cls");printf( "\n\n\n\n\t\tQue valor deseas introducir?\n\n\t\t\t");
scanf( "%d", &valor );
push( &stack,valor );
imprime( stack );
break;
case 2:
system("cls");if( ! validar( stack ) ){
printf( "\n\n\n\n\t\tEl valor sacado de la pila es: %d", pop(&stack));
}imprime( stack );
break;
case 3:
system( "cls" );imprime( stack );
break;
default:
printf( "\n\n\n\t\t ERROR. Introduce un valor adecuado...");...