float addition 2.5 + 2.5 = 4.0? RPN [closed] - c

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Closed 10 years ago.
The code below is my subprogram to do reverse polish notation calculations... basically +, -, *, and /. Everything works in the program except when I try to add 2.5 and 2.5 the program gives me 4.0... I think I have an idea why, but I'm not sure how to fix it... Right now I am reading all the numbers and operators in from command line as required by this assignment, then taking that string and using sscanf to get the numbers out of it... I am thinking that somehow the array that contains the three characters '2', '.', and '5', is not being totally converted to a float... instead i think just the '2' is. Could someone please take a look at my code and either confirm or deny this, and possibly tell me how to fix it so that i get the proper answer? Thank you in advance for any help!
float
fsm (char mystring[])
{
int i = -1, j, k = 0, state = 0;
float num1, num2, ans;
char temp[10];
c_stack top;
c_init_stack (&top);
while (1)
{
switch (state)
{
case 0:
i++;
if ((mystring[i]) == ' ')
{
state = 0;
}
else if ((isdigit (mystring[i])) || (mystring[i] == '.'))
{
state = 1;
}
else if ((mystring[i]) == '\0')
{
state = 3;
}
else
{
state = 4;
}
break;
case 1:
temp[k] = mystring[i];
k++;
i++;
if ((isdigit (mystring[i])) || (mystring[i] == '.'))
{
state = 1;
}
else
{
state = 2;
}
break;
case 2:
temp[k] = '\0';
sscanf (temp, "%f", &num1);
c_push (&top, num1);
i--;
k = 0;
state = 0;
break;
case 3:
ans = c_pop (&top);
if (c_is_empty (top))
return ans;
else
{
printf ("There are still items on the stack\n");
exit (0);
case 4:
num2 = c_pop (&top);
num1 = c_pop (&top);
if (mystring[i] == '+'){
ans = num1 + num2;
return ans;
}
else if (mystring[i] == '-'){
ans = num1 - num2;
return ans;
}
else if (mystring[i] == '*'){
ans = num1 * num2;
return ans;
}
else if (mystring[i] == '/'){
if (num2){
ans = num1 / num2;
return ans;
}
else{
printf ("Error: cannot divide by 0\n");
exit (0);
}
}
c_push (&top, ans);
state = 0;
break;
}
}
}
}
Here is my main program:
#include <stdio.h>
#include <stdlib.h>
#include "boolean.h"
#include "c_stack.h"
#include <string.h>
int main(int argc, char *argv[])
{
char mystring[100];
int i;
sscanf("", "%s", mystring);
for (i=1; i<argc; i++){
strcat(mystring, argv[i]);
strcat(mystring, " ");
}
printf("%.2f\n", fsm(mystring));
}
and here is the header file with prototypes and the definition for c_stack:
#include "boolean.h"
#ifndef CSTACK_H
#define CSTACK_H
typedef struct c_stacknode{
char data;
struct c_stacknode *next;
} *c_stack;
#endif
void c_init_stack(c_stack *);
boolean c_is_full(void);
boolean c_is_empty(c_stack);
void c_push(c_stack *,char);
char c_pop(c_stack *);
void print_c_stack(c_stack);
boolean is_open(char);
boolean is_brother(char, char);
float fsm(char[]);
in response to sixlettervariables:
Part of the assignment is to take an existing string with numbers and decimals in the array and use them to create a float which is what I am doing in these lines of code:
case 1:
temp[k] = mystring[i];
k++;
i++;
if ((isdigit (mystring[i])) || (mystring[i] == '.')) {
state = 1; } else {
state = 2;
}
break;
case 2:
temp[k] = '\0';
sscanf (temp, "%f", &num1);
c_push (&top, num1);
i--;
k = 0;
state = 0;
break;

Answer 1

Your stack stores char data:
typedef struct c_stacknode{
char data;
struct c_stacknode *next;
} *c_stack;
char, by definition, does not store floating point data. Instead, an integer conversion occurs when you call c_push, truncating 2.5 to 2.
You need to update your definition of struct c_stacknode, and its family of related methods, to support float data.

Answer 2

Could you also share the definition of c_stack? It looks like it's a stack of integer type, rounding any floating point input down. That way, 2.5 + 2.5 == 4.

Answer 3

if you define your variables as
int x=2.5;
and
int y=2.5;
An later you make something like
if((x+y)==4.0)
It will be true.
The engine will transform the floats numbers into integers. I guess you are doing something like this.
Look for the variables definitions.