Thread: Parentheses checker with stacks

I have to use stacks to check an input file for parentheses matches.
I have a skeleton...but I am having some problems
Do I have to use a class or struct to do this?
Here is what I have in main

Code:

#include <iostream.h>
#include <fstream.h>
#include <stdlib.h>   // for exit(..)


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

int main()
{
   char c;
   int k;
ifstream f;
  f.open( "input.txt" );

  if( ! f ){
    cout << "Error opening file. Quitting.\n";
    exit(-1);
  }

   //initialize

   stk_init();
      c = getchar();
      putchar(c);

   // loop through file one char at a time
   while (c!=EOF)
   {
     // process one character
     // push (,  pop if ),
     // check stack empty if \n,
     // ignore others
     // if error, move to next line
       if (c == '(')
       {
         stk_push(c);

       }
       else if (c == ')')
       {
            if (c !== '\n')    
            stk_pop(c);
            else if (c == '(')
            stk_push (c);
// pop stack, if empty have missing (
       }
       else if (c == '\n')
       {
         // check on missing )
         // set up for next line
         stk_init();
       }
       if (stk_error()) //skip rest of line

       else // get next char
       {
       }
     } // endwhile
   return 0;
}

my specific question first is
how do I check for the top of the stack?
I know i need to do this for the ')' first but I'm not sure how. Do I need to declare a variable for the top of stack?
Thanks

if std::stack is like <list> and uses the compiler to do something for me...my professor won't let us do that. She wants us to do things the long way first. But thanks for the other tips I kept getting a huge error

Code:

#ifdef __DEPRECATED
#warning This file includes at least one deprecated or antiquated header. \
Please consider using one of the 32 headers found in section 17.4.1.2 of the \
C++ standard. Examples include substituting the <X> header for the <X.h> \
header for C++ includes, or <iostream> instead of the deprecated header \
<iostream.h>. To disable this warning use -Wno-deprecated.
#endif

#endif

our instructor gave us a .h file
what does #define STK_ERROR '?' mean?

yes she wrote the .h file and gave it to us this is it

Code:

/* stack.h: Declarations for a stack of chars */
#define STK_ERROR '?' 

void stk_init();
void  stk_push(char);
char  stk_pop(void);
char  stk_top(void);
int  stk_size(void);
int  stk_error(void);

and this is the .cpp

Code:

/* stack.c: implementation */
#include "stack.h"

/* Private data: */
#define MAX 50 
static int error;   /* error flag */
static char data[MAX];   /* the stack */
static int ptr;         /* stack pointer */

/* Function implementation */

void stk_init() {
   ptr = 0;
   error = 0;
}

void stk_push(char x) {
    if (ptr < MAX) {
        data[ptr++] = x;
        error = 0;
    }
    else
        error = 1;
}

char stk_pop(void) {
    if (ptr > 0) {
        int x = data[--ptr];
        error = 0;
        return x;
    } else {
        error = 1;
        return STK_ERROR;
    }
}

char stk_top(void) {
    if (ptr > 0) {
        error = 0;
        return data[ptr-1];
    } else {
        error = 1;
        return STK_ERROR;
    }
}

int stk_size(void) {
    return ptr;
}

int stk_error(void) {
    return error;
}

I know its alot, but could you comment out this code so I know what it means?

Code:

char stk_top(void) {
    if (ptr > 0) {
        error = 0;
        return data[ptr-1];
    } else {
        error = 1;
        return STK_ERROR;
    }
}

I am in a c++ class (actually my first real c++ class) but we are at the end of the semester and they are introducing data structures and I think this program is mostly in c but compiling with dev? I don't know that is just what I am told...so should i find a C forum?