Deleted zero addition

src/String/s21_memcpy.c

@@ -3,10 +3,7 @@
 void *s21_memcpy(void *dest, const void *src, s21_size_t n) {
   char *source = (char *)src;
   char *destination = (char *)dest;
-  s21_size_t i = 0;
-  for (; i < n; i++) {
-    destination[i] = source[i];
-  }
-  destination[i] = '\0';
+  while (len-- > 0)
+    *destination++ = *source;
   return destination;
 }

src/String/s21_to_lower.c

@@ -15,6 +15,5 @@ void *s21_to_lower(const char *str) {
       copy_str[i] = str[i];
     }
   }
-  copy_str[len] = '\0';
   return (copy_str);
 }

src/String/s21_to_upper.c

@@ -15,6 +15,5 @@ void *s21_to_upper(const char *str) {
       copy_str[i] = str[i];
     }
   }
-  copy_str[len] = '\0';
   return (copy_str);
 }