Thread: finding that expression has balanced parenthese, brackets, braces

Another stack problem.

Now this is not my code. HINT: This one actually works. (ha ha)
I would like to change from using all functions that pass pointers to having only the PUSH function passing a value. Would this work?? And I think I want the functions to match my stack functions from my original STACK program. (which still ain't working -- but will be soon)

Oh, and I would like there to be a better confirmation output instead of just "Correct" when the program finds that the brackets, and braces and parentheses all are balanced for whatever expression is input.

ex. input : {6*5 [y*5] / (a*8)}
output : your expression has balanced symbols

or something like that. What seems like a good output so user knows they input a correct looking expression ??

Also, my instructor said something about using the ASCII codes for the r/l brackets, braces and parentheses. If I did that, would I have to write something like:

instead of

Code:

while (a[i] != NULL)

  {if (a[i] == '(')
    push (&top, '(');
   if (a[i] == ')')
   { if (is_empty(&top))
     {printf("Incorrect\n");
      exit(0);
     }
      pop (&top);
   }
   i++;
  }

write this

Code:

while (a[i] != NULL)
   {if (a[i] == '\40' )        /*   \40 is the character  (  */ 
        push (&top, '\40');
     if (a[i] == '\41' )           /*  \41 is the character  )  */
       {  if (is_empty(&top))
           printf("Incorrect\n");
           exit(0);
       }
      pop (&top);
   }
   i++;
  }

Code:

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

#define N 100

typedef struct {
                char sa[N];
                int count;
}Stack;

void intialize (Stack *);
int is_empty (Stack *);
void push (Stack *, char);
char pop (Stack *);
void cleara(Stack *, int);

int main ()
{
  int i = 0;
  char a[N];
  Stack top;
 
  printf("Please enter a string to be evaluated: ");
 gets(a);

  intialize (&top);
  while (a[i] != NULL)

  {if (a[i] == '(')
    push (&top, '(');
   if (a[i] == ')')
   { if (is_empty(&top))
     {printf("Incorrect\n");
      exit(0);
     }
      pop (&top);
   }
   i++;
  }

  if (!is_empty(&top))
  {printf("Incorrect\n");
   exit(0);
  }
  cleara(&top, N);
  i=0;
  while (a[i] != NULL)
  {if (a[i] == '[')
    push (&top, '[');
   else
   if (a[i] == ']')
   { if (is_empty(&top))
     {printf("Incorrect\n");
      exit(0);
     }
      pop (&top);
   }

   i++;
 }
  if (!is_empty(&top))
  {printf("Incorrect\n");
   exit(0);
  }
  cleara(&top, N);
  i=0;
  while (a[i] != NULL)
  {if (a[i] == '{')
    push (&top, '{');
   if (a[i] == '}')
   { if (is_empty(&top))
     {printf("Incorrect\n");
      exit(0);
     }
      pop (&top);
   }

   i++;
  }
if (!is_empty(&top))
  {printf("Incorrect\n");
   exit(0);
  }
  printf("Correct\n");
  return 0;
}

void intialize (Stack *ptop)
{
  ptop->count = 0;
}

int is_empty (Stack *ptop)
{
  if (ptop->count == 0)
   return 1;

  return 0;
}

void push (Stack *ptop, char p)
{
  ptop->sa[ptop->count] = p;
  (ptop->count)++;
}

char pop (Stack *ptop)
{
  char temp;
  temp = ptop->sa[ptop->count-1];
  (ptop->count)--;
  return temp;
}

void cleara(Stack *ptop, int n)
{ int i;
  for (i=0; i<n; i++)
   ptop->sa[i] = '\0';
}

ok I changed most of what I could think of to change to be in the same format as my earlier stack program in another thread.

I am getting a compilation error (surprise surprise !!)
and don't have a clue as to what it means nor what to fix.

here's the compilation error I get when compiling

28 /accounts/student2/srbkpk/STACK a.out
Please enter a string to be evaluated: {6/(3*4)+(4/2*[45-2])}
40 deleted successfully.
40 deleted successfully.
Segmentation Fault (core dumped)


I don't understand what the cleara function is supposed to do, so I may not have recoded it right to fit my program's spec/variable setup.

What I understand this program to do is have user input a math expression with parentheses, brackets and braces (known as PBB from here on out) and the program only evaluates these symbols. Pushing the open PBB symbol one at a time and if the next PBB symbol is the complementary close PBB, then that is considered balanced.

ex. expression enter = {6/4(2*456)-[46/7]}
first comes across a {
second comes across a (
then comes across a ) so it pops the ( and ) and still
has the { in stack
then comes across a [
then comes across a ] so it pops the [ and ] and still
has the { in stack
then comes across a } so it pops the { and } and
now stack is empty, thus the expression was balanced
correctly.

So is this the correct interruptation of the program and what it is doing??

Code:

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

#define MAX 100

struct node{
   int data;
   struct node * next;
};

struct node *first;

void make_empty(void);
int is_empty (void);
void push (int value);
int pop (void);
void cleara(int);

/***************************************************/
/*      START MAIN                                 */
/***************************************************/

main ()
{
  int i = 0;
  char array[MAX];

  printf("Please enter a string to be evaluated: ");
  gets(array);

  make_empty ();

  while (array[i] != NULL)
  {if (array[i] == '(')
    push ( '(');
   if (array[i] == ')')
   { if (is_empty())
     {printf("Incorrect\n");
      exit(0);
     }
      pop ();
   }
   i++;
  }


  if (!is_empty())
  {printf("Incorrect\n");
   exit(0);
  }

  cleara(MAX);
  i=0;

  while (array[i] != NULL)
  {if (array[i] == '[')
    push ('[');
    else if (array[i] == ']')
   { if (is_empty())
     {printf("Incorrect\n");
      exit(0);
     }
      pop ();
   }

   i++;
 }

  if (!is_empty())
  {printf("Incorrect\n");
   exit(0);
  }

  cleara(MAX);
  i=0;

  while (array[i] != NULL)
  {if (array[i] == '{')
    push ('{');
   if (array[i] == '}')
   { if (is_empty())
     {printf("Incorrect\n");
      exit(0);
     }
      pop ();
   }

   i++;
  }

if (!is_empty())
  {printf("Incorrect\n");
   exit(0);
  }
  printf("Correct\n");

  return 0;
}

/**************************************************/
/*        END MAIN                                */
/**************************************************/

void make_empty(void)
{
  first  = NULL ;
}

int is_empty (void)
{
   return first == NULL;
}

void push(int value)
{
   struct node * new_node;

   new_node=malloc(sizeof(struct node));
   if (new_node == NULL)  {
      printf ("Error in push: stack is full.\n");
      exit (EXIT_FAILURE);
   }

   new_node->data = value;
   new_node->next = first;
   first = new_node;
}

int pop (void)
{
   struct node * top;
   int i;

   if (is_empty())  {
      printf("Error in pop: stack is empty.\n");
      exit (EXIT_FAILURE);
   }

   printf("%d deleted successfully.\n",first->data);
   top = first;
   i = first->data;
   first = first->next;
   free(top);
   return i;
}

void cleara(int n)
{ int i;
  for (i=0; i<n; i++)
   first->data = '\0';
}