functions.c

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

#include "stack.h"

void push(struct node** first, struct node** addAfter, const char val){
    struct node* top;

    top = malloc(sizeof(struct node*));
    top->val = val;

    if(*first == NULL){
        *first = top;
        *addAfter = *first;
    }
    else{
        (*addAfter)->next = top;
        *addAfter = top;
    }

}

char pop(struct node** first, struct node** last){
    struct node* t;

    if(*first == *last){
        *first = *last = NULL;
        return '\0';
    }

    for(t = *first; t != *last; t = t->next){
        if(t->next == *last){
            t->next = NULL;
            *last = t;
            break;
        }
    }

    return t->val;
}

int isEmpty(struct node** first){
    return *first == NULL;
}

void showStack(struct node* first){
    struct node* t = NULL;

    for(t = first; t != NULL; t = t->next){
        printf("%c", t->val);
    }

    printf("\n");
}

int match(const char current, const char last){
    int current_ascii, last_ascii;
    current_ascii = current;
    last_ascii = last;

    if(current_ascii == (last_ascii + 1)){
        return 1;
    }

    return 0;
}

functions.h

#ifndef HGUARD_FUNC
#define HGUARD_FUNC

int isEmpty(struct node** first);
void push(struct node** first, struct node** last, const char val);
char pop(struct node** first, struct node** last);
void showStack(struct node* first);
int match(char current, char last);

#endif

main.c

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

#include "stack.h"
#include "functions.h"

struct node *first = NULL, *last = NULL;


int main(void){
    char* stringTest = " ((( ()) ))";

    int i;
    for(i = 0; i < strlen(stringTest); i++){
        if(last == NULL){
            push(&first, &last, stringTest[i]);
        }
        else if(match(stringTest[i], last->val)){
            pop(&first, &last);
        }
        else{
            push(&first, &last, stringTest[i]);
        }
    }

    if(isEmpty(&first)){
        printf("Matched!\n");
    }
    else{
        showStack(first);
    }
    return EXIT_SUCCESS;
}

stack.h

#ifndef H_GUARD_STACK
#define H_GUARD_STACK

struct node{
    char val;
    struct node* next;
};

#endif