Thread: Parentheses Checker

Code:

Program is supposed to check for balanced parentheses which are (), {}, [] using a vector
First read in the number of lines user wishes to test
Return Yes if balanced, No if unbalanced
Missing conditions to check for unbalanced parentheses
Program doesn't catch left parentheses returns Yes
Pairs wrong parentheses together, (} returns Yes, should be No
Cases with incorrect output
(}, (], ))), }}}, ]]], just a space or nothing entered
Looking for answers to how I can correctly catch the cases I've missed

Code:

#include <stdio.h>
#include <stdlib.h>
#include "char_vector.h"


int main( int argc, char * argv [])
{
  int i, num;
  char c;
  scanf("%d", &num);
  scanf("%c", &c);


  for(i = 0; i < num; i++)
    {
      MY_VECTOR vector = my_vector_init_default();
      do
        {
          scanf("%c", &c);
            if (c == '(' || c == '[' || c == '{')
              {
                char_my_vector_push_back(vector, c);
              }


            if (c == ')' || c == ']' || c == '}')
              {
                my_vector_pop_back(vector);
              }
          }while(c != '\n');


      if (my_vector_size(vector) == 0)
        {
          printf( "Yes\n");
        }
      else
        {
          printf( "No\n");
        }
      my_vector_destroy(&vector);
    }
return 0;
}

Originally Posted by whiteboyfly

My check to see if the vector is empty is still off as reading in a space still outputs Yes.

This is as it should be. If you neither push nor pop into the vector, then the size will remain at 0.

And if you've written pop_back at all correctly, it will give you the character that is popped off, so you can compare with the just-read-in character and see what's what.

Originally Posted by whiteboyfly

My understanding: Push is when the character read in is put onto the stack. Pop is when the character on top of the stack is taken off the stack. These functions work as LIFO last in first out. If I enter ()))) then ) would be the first character popped.

My confusion: Where does the character that is popped go? How can I compare it to other characters on the stack? If I enter ()(} I should immediately get a mismatch when ( is encountered but I'm confused on how to make this comparison.
Thanks in advance.

You shouldn't be pushing the the end brackets at all, at least not how I understand the problem. You should be pushing every open bracket to the stack and then whenever you encounter a ending bracket you simply pop a character from the stack and make sure it is the corresponding open bracket.

A lot of people say to imagine a stack of plates as an analogy for a stack, you usually only ever put a plate on top and take a plate from the bottom. That said I don't really like this approach because I feel like the bottom plates will build up dust over time and so I'd need to wash them before use if I had a dinner party.

EDIT: Also I'm incredibly sick of this 'code must be in code tags' rule which tells me off for posting 6 character literals in my english text .

Thanks for the reply, maybe I should be more clear how do I go about making the comparison of popped characters to corresponding characters? This is my best attempt at a guess:

Code:

if (my_vector_pop_back(vector) == '(' || my_vector_pop_back(vector) == '[' || my_vector_pop_back(vector) == '{' )
  {
    //balanced return Yes                                                                                                                                                          
  }
 else
   {
     //unbalanced return No                                                                                                                                                        
   }