diff --git a/k&r/04-funcs-and-prog-struct/04-find/find-opt.c b/k&r/04-funcs-and-prog-struct/04-find/find-book.c
similarity index 67%
rename from k&r/04-funcs-and-prog-struct/04-find/find-opt.c
rename to k&r/04-funcs-and-prog-struct/04-find/find-book.c
index 047dae4..a251088 100644
--- a/k&r/04-funcs-and-prog-struct/04-find/find-opt.c
+++ b/k&r/04-funcs-and-prog-struct/04-find/find-book.c
@@ -1,21 +1,19 @@
 #include <stdio.h>
-#include <string.h>
 
 #define MAXLINE 1000 /* maximum input line length */
 
 int getln(char line[], int lim);
-int strindex(char source[], char searchfor[], int slen);
+int strindex(char source[], char searchfor[]);
 
 /* find: prints lines containing pattern, returns number of matching lines */
 int find(char *pattern, char lineno_flag, char except_flag)
 {
     char line[MAXLINE];
     int found = 0;
-    int slen = strlen(pattern);
     long lineno;
 
     for (lineno = 1; getln(line, MAXLINE) > 0; lineno++)
-        if ((strindex(line, pattern, slen) >= 0) != except_flag) {
+        if ((strindex(line, pattern) >= 0) != except_flag) {
             if (lineno_flag)
                 printf("%ld:", lineno);
             printf("%s", line);
@@ -36,15 +34,14 @@ int getln(char *s, int lim)
 }
 
 /* strindex: return index of t in s, -1 if none */
-int strindex(char s[], char t[], int slen)
+int strindex(char s[], char t[])
 {
-    int i, j;
-
-    for (i = j = 0; s[i]; i++)
-        if (s[i] != t[j])
-            j = 0;
-        else if (++j == slen) { // found match
-            return i - slen + 1;
-        }
+    int i, j, k;
+    for (i = 0; s[i]; i++) {
+        for (j=i, k=0; t[k] && s[j] == t[k]; j++, k++)
+            ;
+        if (k > 0 && !t[k])
+            return i;
+    }
     return -1;
 }