//
//  rpn.c
//
//
//  Created by Douglas Frisk on 2008-09-13.
//  Copyright 2008 __MyCompanyName__. All rights reserved.
//
/* RPN calculator. */

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <ctype.h>

#ifndef SIZE
#define SIZE 10
#endif

#ifndef NBR
#define NBR_SIZE 10
#endif

struct the_stack
{
	int top;
	int data[SIZE];
};

static char*	progname;		// program name set in main from argv.
static struct the_stack stack = { 1 };

int nbr = 0;



void error(char* msg, ...)
{
	va_list		ap;

	va_start(ap, msg);
	fprintf(stderr, "%s: error: ", progname);
	vfprintf(stderr, msg, ap);
	va_end(ap);
	exit(1);
}

void calculate(char op)
{
	int nbr1, nbr2;
	nbr1 = pop();
	nbr2 = pop();
	int result;
	switch(op)
	{
		case '+' :
			push(nbr1 + nbr2);
			break;
		case '-' :
			push(nbr2 - nbr1);
			break;
		case '*' :
			push(nbr1 * nbr2);
			break;
		case '/' :
			if(nbr1 == 0)
			{
				error("Divide by zero");
			}
			push(nbr2 / nbr1);
			break;
		default :
			printf("%c is not a legal operand.\n", op);
	}
}

void push(int n)
{
	if(stack.top == SIZE)
	{
		printf("Your stack is full. No room to push.\n");
	}
	stack.data[(stack.top)++] = n;
}

int pop()
{
	if(stack.top==0)
	{
		printf("Empty stack, nothing to pop.\n");
	}
	return stack.data[--(stack.top)];
}

int nbr_parse(char c)
{
	char nbr[NBR_SIZE], *endptr;
	int cnt = 0;
	while(c != EOF && !isspace(c))
	{
		nbr[cnt++] = c;
		c = getchar();
	}
	nbr[cnt] = '\0';

	int return_value = strtol(nbr, &endptr, 10);

	if(*endptr!='\0')
	{
		error("Syntax error\n");
	}
	return return_value;
}

int main(int argc, char** argv)
{
	progname = argv[0];
	printf("Enter expression:\n");
	char c;
	int prev = 0;
	while((c=getchar()) != EOF)
	{
		switch(c)
		{
			case '+' :
			case '-' :
			case '*' :
			case '/' :
				calculate(c);
				break;
			case '\n' :
				printf("Result: %d\n", pop());
				break;
			default :
				if(!isspace(c))
				{
					push(nbr_parse(c));
				}
		}
	}
}