Check for balanced parentheses in an expression

PROBLEM :

Given an expression string exp, examine whether the pairs and the orders of “{“,”}”,”(“,”)”,”[“,”]” are correct in exp.
For example, the program should print 'balanced' for exp = “[()]{}{[()()]()}” and 'not balanced' for exp = “[(])”



Input:

The first line of input contains an integer T denoting the number of test cases.
Each test case consist of a string of expression, in a separate line.

Output:

Print 'balanced' without quotes if pair of parenthesis are balanced else print 'not balanced' in a separate line.


Constraints:

1 = T = 30
1 = |s| = 100


Example:

Input:
3
{([])}
()
()[]

Output:
balanced
balanced
balanced

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SIMPLE c++ IMPLEMENTATION :
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#include<iostream>
using namespace std;
#include<string.h>

typedef struct STACK
{
    char data ;
    struct STACK *next ;
}stack ;

void push_stack(stack **,char ) ;
char pop_stack(stack **) ;
int compare(char,char ) ;

int main()
 {
int t,no,i,flag,k,len ;
char ch[100],ele ;
cin>>t ;
while(t--)
{
   cin>>ch ;
   len=strlen(ch) ;
 
 
   stack *s=NULL ;
   flag=1 ;
   for(i=0;i<len;i++)
   {
       if((ch[i]=='[')||(ch[i]=='{')||(ch[i]=='('))
           push_stack(&s,ch[i]) ;
         
       else if((ch[i]==']')||(ch[i]=='}')||(ch[i]==')'))
       {
           ele=pop_stack(&s) ;
           if(ele=='#')
           {
               flag=0 ;
               break ;
           }
         
           k=compare(ele,ch[i]) ;
           if(k==0)
           {
               flag=0 ;
               break ;
           }
       }
   }
    if(s!=NULL)
           flag=0 ;
         
    if(flag==0)
       cout<<"not balanced" ;
    else
       cout<<"balanced" ;
     
      cout<<endl ;
}
return 0;
}

void push_stack(stack **s,char ch)
{
    stack *temp ;
    temp=(stack*)malloc(sizeof(stack)) ;
    temp->data=ch ;

    temp->next=(*s) ;
    (*s)=temp ;
}

char pop_stack(stack **s)
{
    stack *temp ;
    if((*s)==NULL)
        return '#' ;
       
    temp=(*s) ;
    (*s)=temp->next ;
    char ch=temp->data ;
    free(temp) ;
    return ch ;
}

int compare(char ch1,char ch2)
{
    if((ch1=='[')&&(ch2==']'))
        return 1 ;
    else if((ch1=='{')&&(ch2=='}'))
        return 1 ;
    else if((ch1=='(')&&(ch2==')'))
        return 1 ;
       
    return 0 ;
}

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