Thread: Help with Postfix Calculator Project

Hello, I am new to posting on this board, but have been reading posts for a few weeks now. I have searched through the FAQ and old posts and can't find the answer to my question.

I have to create a postfix calcuator in C using linked lists, along with push and pop functions. I am able to get output with the code that I have done thus far, but it's not right. If someone could please provide me some pointers on this, I would greatly appreciate it! Thank you very much!

Code:

// Calc2.cpp : Defines the entry point for the console application.
//

#include "stdio.h"
#include "stdlib.h"
#include "stdafx.h"
#include "conio.h"
#include "malloc.h"
#include "ctype.h"
#include "string.h"

#define LINE_LEN 81


typedef int stack_element_t;

typedef struct stack_node_s {
	stack_element_t element;
	struct stack_node_s *restp;
} stack_node_t;

typedef struct {
	stack_node_t *topp;
} stack_t;

void push(stack_t *sp, stack_element_t c);
stack_element_t pop(stack_t *sp);

int _tmain(int argc, _TCHAR* argv[])
{

	char ans2[LINE_LEN];
	stack_t ans={NULL};
	int w, x, y, z, solution;
	
	

	printf("Enter a postfix notation expression");
	printf("\n:");
	gets(ans2); // Get the answer
    w=0;
	
	for (z=0;z<=80;z++)
		if (isdigit(ans2[z])){
			w=(w*10)+ans2[z];
			
		} else if (ans2[z] == '*' || ans2[z] == '+' || ans2[z] == '/' || ans2[z] == '%' || ans2[z] == '-' ) {
			x=pop(&ans); // pop the first portion of the stack (number)
			y=pop(&ans); // pop the second portion of the stack (number) 
			switch(ans2[z])
			{
			case '+': solution = x + y; break;
			case '-': solution = x - y; break;
			case '/': solution = x / y; break;
			case '*': solution = x * y; break;
			case '%': solution = x % y; break;
			}
			printf("=%d", solution); 
		} else if (ans2[z]==' '){
			push(&ans, w);/* Builds the stack based on the user's entry */
			w=0;
		}else if (ans2[z]=='\0'){
			printf("\nPress any key...");
			getch();
			return 0;
		}
 	
}	

void push(stack_t *sp, stack_element_t c)
{
	stack_node_t *newp; 
	/* pointer to new stack node */

	newp = (stack_node_t *) malloc(sizeof (stack_node_t));
	newp->element =c;
	newp->restp = sp->topp;
	sp->topp = newp;
}

stack_element_t pop(stack_t *sp)
{
	stack_node_t *to_freep;
	stack_element_t answer;
	to_freep = sp->topp;
	answer= to_freep->element;
	sp->topp = to_freep->restp;
	free(to_freep);

	return (answer);
}

I'm not sure if this will explain the reason why some of the code may have looked a bit different, but I am using Visual Studio .NET edition's version of Visual C++ to make this program. When I do that, it automatically generates the main function as int _tmain(int argc, _TCHAR* argv[])

Thanks for letting me about the distinction between the "" and <> for the header files. I thought that could be used interchangably...

I chose to use gets because that the was the only that I was aware of to be able to grab an entire line of user input as one string. (Other than fgets, which I don't fully grasp). If there is a better method, I am open to that suggestion.

In terms of sample output, here goes:

User inputs:

1 1 +

The user gets:

=98

User inputs:

2 3 *

The user gets:

2550


I hope that this helps.. thanks again..

Thank you very very much.. that works great! I really do appreciate the help!