Thread: Stack that evaluates postfix expressions

hello..my goal here is to take the stack program that i already have and use it to evaluate postfix expressions from a file. I need help figuring out how to modify the stack to work with integers and evaluate the expressions. Any suggestions?

Code:

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

#define TRUE 1
#define FALSE 0
struct info_node
{
	int weight ;
	struct info_node* next ;

} ;

struct nstack
{
	struct info_node* top ;
} ;


void create_stack(struct nstack*) ;
int empty_stack(struct nstack*) ;
void push_stack(struct nstack* , struct info_node*) ;

struct info_node* pop_stack( struct nstack* ) ;



int main()
{
FILE* infile ;
int a = 0 ;
int num = 0 ;
struct nstack even_Stack ;
struct nstack odd_Stack ;
struct info_node* pnew_node = NULL ;
struct info_node* ppop_node = NULL ;


				create_stack(&even_Stack) ;
				create_stack(&odd_Stack) ;

				infile = fopen("express.txt", "r") ;

				while (!feof( infile ) )
				{
					a++ ;
					fscanf(infile, "%d" , &num) ;

					pnew_node = (struct info_node* ) malloc(sizeof(info_node) ) ;
					
					pnew_node->weight = num ;
					pnew_node->next = NULL ;

					if( (num % 2) == 0 )
						push_stack(&even_Stack, pnew_node) ;
					else
						push_stack(&odd_Stack, pnew_node) ;


				}

	while( !empty_stack(&even_Stack) )
	{
		ppop_node = pop_stack(&even_Stack) ;
		num = ppop_node-> weight ;

		printf("%d ", num ) ;

		a++;
		if( (a % 20) == 0 )
			printf("\n") ;
		
	}
	printf("\n\n") ;
	a = 0 ;
		while( !empty_stack(&odd_Stack) )
	{
		ppop_node = pop_stack(&odd_Stack) ;
		num = ppop_node-> weight ;

		printf("%d ", num ) ;

		a++;
		if( (a % 20) == 0 )
			printf("\n") ;
		
	}


		fclose(infile) ;
	return (0) ;


} //end of func main

void create_stack(struct nstack* pnstack)
{
	pnstack->top = NULL ;
	return ;

} //end of func create_stack

int empty_stack(struct nstack* pnstack)
{
	if (pnstack->top == NULL)
		return (TRUE) ;
	else
		return (FALSE) ;

} //end of func empty_stack

void push_stack(struct nstack* pnstack, struct info_node* pnnode)
{
	if(empty_stack(pnstack))
	{
		pnstack->top = pnnode ;
		pnnode->next = NULL ;
	}
	else
	{
		pnnode->next = pnstack->top ;
		pnstack->top = pnnode ;
	}
	return ;

} //end of func push_stack

struct info_node* pop_stack( struct nstack* pnstack )
{
	struct info_node* prnode = NULL ;

	if(empty_stack(pnstack) )
		printf("ERROR: STACK IS EMPTY!!! \n") ;
	else
	{
		prnode = pnstack->top ;
		pnstack->top = pnstack->top->next ;
		prnode->next = NULL ;
	}
	
	return( prnode ) ;

} // end of func pop_stack

int calc(int operand1, int oper, int operand2)
{
	//Local Declaration
	int result = 0 ;

	//Statements

	switch(oper)
	{
	case '+' : result = operand1 + operand2;
	break ;
	case '-' : result = operand1 - operand2;
	break ;
	case '*' : result = operand1 * operand2;
	break ;
	case '/' : result = operand1 / operand2;
	break;
	} //end of switch(oper)
	return (result) ;
} //end of function calc()

Also these are the expressions i am supposed to read in from a file(express.txt):
1 2 3 * 4 / +
1 2 3 4 / * +
1 2 + 3 * 4 /
1 2 + 4 3 / *
1 2 3 * + 4 /
4 3 / 1 2 + *
6 7 8 / 9 * -
6 7 8 9 * / -
6 7 - 8 / 9 *
6 7 - 9 8 * /
6 7 8 / - 9 *
8 9 * 6 7 - /