Simple brainfuck interpreter

bf.c

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define NUL '\0'
 
struct Loop {
    char *start;
    char *end;
    struct Loop *next;
};
 
struct Loop* current_loop = NULL;
void get_loop(char *start) {
    struct Loop *n = current_loop;
    if (n == NULL || n->start != start) {
        current_loop = (struct Loop *) malloc(sizeof(struct Loop));
        current_loop->next = n;
        current_loop->start = start;
    }
}
 
void set_end(char *end) {
    current_loop->end = end;
}
 
char *goto_start() {
    return current_loop->start - 1;
}
 
char *pop_loop(char* code_seg) {
    int counter = 0;
    char *end = current_loop->end;
    char *ip = current_loop->start;
    struct Loop *n = current_loop;
    current_loop = current_loop->next;
    free(n);
 
    if (end == NULL) {
        while (*++ip != ']' || counter != 0) {
            if (*ip == '[') counter++;
            if (*ip == ']') counter--;
        }
        return ip;
    }
 
    return end;
}
 
int main(int argc, char **argv) {
    
    FILE *fin = NULL;
    char c, code_seg[3000], data_seg[3000], *ip, *dp;
 
    memset(data_seg, 0, 3000);
 
    if (argc < 2) {
        printf("bf -- brainfuck interpreter\n");
        printf("usage: bf myfile.bf\n");
        return 1;
    }
 
    fin = fopen(argv[1], "r");
    ip = code_seg;
    while((c = fgetc(fin)) != EOF)
        if (c == '+' || c == '-' || c == '[' || c == ']' 
                || c == '.' || c == ',' || c == '<' || c == '>') {
            *ip++ = c;
        }
 
    fclose(fin);
 
    *ip = NUL;
    
    dp = data_seg;
    for(ip = code_seg; *ip != NUL; ip++) {
        switch(*ip) {
            case '+':
                ++*dp;
                break;
            case '-':
                --*dp;
                break;
            case '[':
                get_loop(ip);
                if (*dp == NUL)
                    ip = pop_loop(code_seg);
                break;
            case ']':
                set_end(ip);
                ip = goto_start();
                break;
            case '>':
                ++dp;
                break;
            case '<':
                --dp;
                break;
            case '.':
                putchar(*dp);
                break;
            case ',':
                *dp = getchar();
                break;
            default:
                break;
        }
    }
 
    return EXIT_SUCCESS;
 
}