application of stack parenthisis infix to postfix

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

#define TRUE 1
#define FALSE 0

typedef unsigned char BOOLEAN;

typedef struct NODE_tag
{
    char data;
    struct NODE_tag *llink;
    struct NODE_tag *rlink;
}NODE;

NODE *getnode()
{
    NODE *NEW;
    NEW=(NODE *)malloc(sizeof(NODE));
    NEW->llink=NULL;
    NEW->rlink=NULL;
    return NEW;
}

typedef struct stack
{
    NODE *TOP;
}STACK;

STACK initialise(STACK S)
{
    S.TOP=NULL;
    return S;
}

BOOLEAN isFull(STACK S)
{
    NODE *NEW;
    NEW=getnode();
    if(NEW==NULL)
    {
        return TRUE;
    }
    else
    {
    return FALSE;
    free(NEW);
    }
}

BOOLEAN isEmpty(STACK S)
{
    if(S.TOP==NULL)
    {
        return TRUE;
    }
    else
    {
        return FALSE;
    }
}


STACK Push(STACK S, char x)
{
    NODE *New;
    New = getnode();
    if(New==NULL)
        {
            printf("\n STACK overflow error");
            return S;
        }
    New->data = x;
    if (S.TOP== NULL)
    {
        S.TOP = New;
    }
    else
    {
        New->rlink=S.TOP;
        S.TOP->llink = New;
        S.TOP=New;
    }
    return S;
}

STACK Pop(STACK S, char *x)
{
    NODE *Del;
    if (S.TOP == NULL)
    {
        printf("\n STACK underflow error");
        return S;
    }
    Del = S.TOP;
    S.TOP = Del->rlink;
    if (S.TOP!=NULL)
    {
        S.TOP->llink = NULL;
        Del->rlink = NULL;
    }
    *x = Del->data;
    free(Del);
    return S;
}

void display(STACK S)
{
    NODE *Ptr=S.TOP;
    if (S.TOP == NULL)
    {
        printf("\nEmpty STACK");
        return;
    }
    printf("\nCurrent content of the STACK:");
    while(1)
    {
        if (Ptr==NULL) return;
        printf("%c ", Ptr->data);
        Ptr=Ptr->rlink;
    }
    printf("\n");
}

BOOLEAN brackets(char c)
{
    if(c=='(' || c==')' || c=='{' || c=='}' || c=='[' || c==']')
    return TRUE;
    else
    return FALSE;
}
void arrange(char *ch)
{
    STACK S;
    int i=0;
    char f;
    S = initialise(S);
    while(ch[i]!='\0')
    {
        display(S);
        if(brackets(ch[i])==TRUE)
        {
            switch (ch[i])
            {
                case '(':
                S=Push(S,ch[i]);
                break;
                case '{':
                S=Push(S,ch[i]);
                break;
                case '[':
                S=Push(S,ch[i]);
                break;
                case ']':
                S=Pop(S,&f);
                break;
                case '}':
                S=Pop(S,&f);
                break;
                case ')':
                S=Pop(S,&f);
                break;
            }
        }
        else
        {
            S=Pop(S,&f);
        }
        i++;
    }
if(S.TOP->rlink==NULL)
{
 return;
}
}
int main()
{
    char st[250];
    int i;
    printf("enter a suquence ");
    gets(st);
    for(i=0;;i++)
    {
        if(st[i]=='\0')
        {
            st[i]=' ';
            st[i+1]='\0';
            break;
        }
    }
    arrange(st);
    return 0;
}