Infix to postfix conversion using linked list in c

Can anyone please help me with this code? I'm trying to convert from infix to postfix using a linked list. With an array, I can easily solve this, that solution is also similar to this one. But I'm not getting why this is not working. My guess is I've done anything wrong in this part -

if (precedence(ch) > precedence(top->data))
{
    push(ch);
}
else
{
    while (precedence(ch) <= precedence(top->data))
    {
        postfix = insert(postfix, pop());
    }
    push(ch);
}

Here is the complete code. Thanks.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_SIZE 100

struct Node
{
    char data;
    struct Node *next;
};

struct Node *top = NULL;
struct Node *postfix = NULL;

void push(char ch);
char pop();
int is_operator(char ch);
int precedence(char ch);
void convert(char *infix);
struct Node *insert(struct Node *head, char ch);
void print(struct Node *head);

int main()
{
    char infix[MAX_SIZE] = "(A+B^C)*D+E^5";
    printf("Infix: %s\n", infix);
    convert(infix);
    printf("Postfix: ");
    print(postfix);
}

void convert(char *infix)
{
    int i, len = strlen(infix);
    char ch;

    for (i = 0; i < len; i++)
    {
        ch = infix[i];
        if (is_operator(ch) == 0)
        {
            postfix = insert(postfix, ch);
        }
        else
        {
            if (ch == '(')
            {
                push(ch);
            }
            else
            {
                if (ch == ')')
                {
                    while (top->data != '(')
                    {
                        postfix = insert(postfix, pop());
                    }
                    pop();
                }
                else
                {
                    if (precedence(ch) > precedence(top->data))
                    {
                        push(ch);
                    }
                    else
                    {
                        while (precedence(ch) <= precedence(top->data))
                        {
                            postfix = insert(postfix, pop());
                        }
                        push(ch);
                    }
                }
            }
        }
    }
    while (top != NULL)
    {
        postfix = insert(postfix, pop());
    }
}

int is_operator(char ch)
{
    switch (ch)
    {
    case '+':
    case '-':
    case '*':
    case '/':
    case '^':
    case '(':
    case ')':
        return 1;
    default:
        return 0;
    }
}

int precedence(char ch)
{
    switch (ch)
    {
    case '+':
    case '-':
        return 2;
    case '*':
    case '/':
        return 3;
    case '^':
        return 4;
    default:
        return 1; // if (, ), or empty
    }
}

void push(char ch)
{
    struct Node *newP = (struct Node *)malloc(sizeof(struct Node));
    newP->data = ch;
    newP->next = top;
    top = newP;
}

char pop()
{
    char ch = top->data;
    struct Node *temp = top;
    top = temp->next;
    free(temp);
    temp = NULL;
    return ch;
}

struct Node *insert(struct Node *head, char ch)
{
    struct Node *newP = (struct Node *)malloc(sizeof(struct Node));
    newP->data = ch;
    newP->next = NULL;
    if (head == NULL)
    {
        head = newP;
    }
    else
    {
        struct Node *temp = head;
        while (temp->next != NULL)
        {
            temp = temp->next;
        }
        temp->next = newP;
    }
    return head;
}

void print(struct Node *head)
{
    while (head != NULL)
    {
        printf("%c", head->data);
        head = head->next;
    }
    printf("\n");
}