/*
 * Postfix (reverse Polish) calculator
 * uses switch and no arithmetic/math functions
 */
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include "stack.h"

/*
 * maximum length of input line
 */
#define	MAXLINE	1000

/*
 * the main routine
 */
int main(void)
{
	char line[MAXLINE];	/* input line */
	char *l;		/* used to get input characters */
	int v1, v2;		/* operands for current operation */

	/*
	 * process the input line by line
	 */
	while(fgets(line, MAXLINE, stdin) != NULL){
		/*
		 * got line; now walk it char by char
		 */
		for(l = line; *l; l++){
			/* skip white space */
			if (isspace(*l))
				continue;
			/* now act based on the character you see */
			switch(*l){
			case '0': case '1': case '2':	/* number */
			case '3': case '4': case '5':
			case '6': case '7': case '8':
			case '9':
				push(*l - '0');
				break;
			case '+':			/* add */
				if (pop(&v1) == 0)
					continue;
				if (pop(&v2) == 0)
					continue;
				push(v2 + v1);
				break;
			case '-':			/* subtract */
				if (pop(&v1) == 0)
					continue;
				if (pop(&v2) == 0)
					continue;
				push(v2 - v1);
				break;
			case '*':			/* multiply */
				if (pop(&v1) == 0)
					continue;
				if (pop(&v2) == 0)
					continue;
				push(v2 * v1);
				break;
			case 'p':			/* print stack */
				if (pop(&v1) == 0)
					continue;
				printf("%d\n", v1);
				push(v1);
				break;
			case 'P':			/* print stack */
				printstack();
				break;
			default:			/* unknown */
				fprintf(stderr, "Unknown operand/operator '%c'\n", *l);
				break;
			}
		}
	}

	/*
	 * all done!
	 */
	return(0);
}