To find the longest substring with unique characters in a given string

#include <stdio.h>  
#include <string.h>  
  
typedef struct {  
  
    const char \*start;  
    size\_t len;  
  
}Substring;  
  
  
Substring longestSubstring(const char \*s){  
  
    Substring ret = {s, 1};  
      
    Substring cur = {s, 1};  
          
    size\_t i, len = strlen(s);  
      
    const char \*p = NULL;  
      
    for(i = 1; i < len; ++i){  
      
            p = memchr(cur.start, s\[i\], cur.len);  
              
            if(p){  
              
                    if(cur.len > ret.len)  
                            ret = cur;  
                                  
                    cur.len -= (p - cur.start) + 1;  
                      
                    cur.start = p + 1;  
            }  
              
            cur.len++;  
      
    }  
  
    if(cur.len > ret.len)  
            ret = cur;  
      
  
    return ret;  
}  
  
  
int main(){  
  
    char s\[64\];  
      
    scanf("%s", s);  
  
    Substring sub = longestSubstring(s);  
      
    ((char \*)sub.start)\[sub.len\] = '\\0';  
  
    printf("%s\\n", sub.start);  
  
    return 0;  
  
}