字符串去重

#include <stdio.h>
#include <string.h>
#define M 500

void fun(char *a, void (*p)(char *, void (*q)(char *, char *)), void  (*q)(char *, char *))
{
    char *t;
    for (t = a + 1; *t != '\0'; ++t)
    {
        if (*t == *(t - 1))
        {
            if (*t != '\0')
            {
                *t = ' ';
                p(t, q);
                t--;
            }
            else
            {
                return ;
            }
        }
        else if (*t != *(t - 1) && *t == *(t + 1))
        {
            if (*(t + 1) != '\0')
            {
                *(t + 1) = ' ';
                p(t + 1, q);
                t--;
            }
            else
            {
                return ;
            }
        }
    }
}
void fun2(char *a, void  (*q)(char *, char *))
{
    char *t;
    t = a + 1;
    for (; *t != '\0'; ++t)
    {
        q(t, t - 1);
    }
    q(t, t - 1);
}
void swap(char *a, char *b)
{
    char c;
    c = *a;
    *a = *b;
    *b = c;
}
int main(int argc, char const *argv[])
{
    char str[M] = "asss dffff ggggg";
    gets(str);
    void (*q)(char *, char *);
    void (*p)(char *, void (*q)(char *, char *));
    q = swap;
    p = fun2;
    fun(str, p, q);
    puts(str);
    return 0;
}