diff --git a/21-shell/libc/string.c b/21-shell/libc/string.c
index 69262d7..e29db34 100644
--- a/21-shell/libc/string.c
+++ b/21-shell/libc/string.c
@@ -17,15 +17,18 @@ void int_to_ascii(int n, char str[]) {
     reverse(str);
 }
 
+
 /* K&R */
-void reverse(char s[]) {
-    int c, i, j;
-    for (i = 0, j = strlen(s)-1; i < j; i++, j--) {
-        c = s[i];
-        s[i] = s[j];
-        s[j] = c;
+void reverse(char s[]){
+    char tmp;
+    int l, j;
+    l  = strlen(s);
+    for (j = 0; j < l/2; j++){
+        tmp = s[l - j - 1];
+        s[l - j - 1] = s[j];
+        s[j] = tmp;
     }
-}
+} 
 
 /* K&R */
 int strlen(char s[]) {