[r.stiltskin]

Martyn.Rae, on 11 April 2010 - 12:32 AM, said:

You are returning n but n is never assigned anything.

(Not sure why Martyn.Rae said that.)


A few problems are apparent. First, in main:

int main(void)
{
    char* next_token="";
    printf("This is the RPN calculator\n"); 

    next_token=get_next_token();
// ...

Note that you are assigning the pointer next_token to a variable that is local to get_next_token(), so it is out of scope as soon as that function finishes, i.e. the value that next_token points to can vanish at any moment. To fix this:
in main: declare next_token as a char, not a char*, and
in get_next_token(): return the value of the token instead of a pointer (and change the return type of the function accordingly).


Next problem, here:

#include <stdio.h>
#include <ctype.h>
#include "inputter.h"
#include "stack.h"

char* get_next_token(void)
{
// ...

It looks like this file is inputter.h, so you shouldn't have #include "inputter.h" at the top of it.

Next:

char* get_next_token(void)
{
    char next_ch[1000];

I already mentioned above that you should change the return type of this function. Also, why are you declaring next_ch to be a 1000-element array when it is supposed to get only 1 token at a time?

Next:

    do
    {
        *next_ch = getchar();

        if (tolower((int)*next_ch) == 'q')
        {
            // User wants to quit.
            break;
        }

        if ((*next_ch == '\n'))
        {
            break;
        }

Immediately after *next_ch = getchar(); you should put an extra getchar(); to retrieve and discard the newline character, and remove the block beginning with if ((*next_ch == '\n')). Also, there is no reason to cast *next_ch to an int in the call to tolower(). (You perform this unnecessary casting in a number of other places as well.)


Next:

       if (isdigit(*next_ch) ||
            (*next_ch == '+') ||
            (*next_ch == '-') ||
            (*next_ch == '*') ||
            (*next_ch == '/') ||
            (*next_ch == '=')    )
        {
            printf("entered is %s\n", next_ch);
            ++*next_ch;
            i++;

here, if an operator is entered, you are discarding it instead of returning it. Why?


I also noticed that at the beginning of the file that seems to be calculate.h, you have (erroneously) #include "calculate.h".


edit: Most of my comments above are based on the assumption that you want to retrieve just 1 char at a time since that's what you seem to be doing. If, on the other hand, you want to be able to retrieve several chars at once (e.g. strings of digits), then the return type should be neither a char nor a char*. I would suggest that you make it return an int, representing the number of chars of input, AND you should create a char array in main, AND pass that array to get_next_token and store the user's input in it. In other words, in that case the function signature should look like this:

int get_next_token( char* token )

This post has been edited by r.stiltskin: 11 April 2010 - 12:36 AM