#include <stdio.h>

#define MAXSTACKSIZE 100

double stack[MAXSTACKSIZE];

/* stack "pointer" -- "points" to the top value */
int sp = 0;

/* push a value onto the stack */
void push( double value ) {
       if ( sp < MAXSTACKSIZE ) {
/*              stack[sp++] = value; */
               stack[sp] = value;
               sp++;
       } else {
               printf( "ERROR: Stack is full.\n" );
       }
}

/* pop and return top value from the stack */
double pop() {
       if ( sp > 0 ) {
/*        return stack[--sp]; */
               sp--;
               return stack[sp];
       } else {
               printf( "ERROR: Stack is empty\n" );
       }
}