diff --git a/iteration.Rmd b/iteration.Rmd
index 4ee0199..305e8b2 100644
--- a/iteration.Rmd
+++ b/iteration.Rmd
@@ -128,7 +128,7 @@ That's all there is to the for loop! Now is a good time to practice creating som
 1.  Eliminate the for loop in each of the following examples by taking 
     advantage of a built-in function that works with vectors:
     
-    ```{r}
+    ```{r, eval = FALSE}
     out <- ""
     for (x in letters) {
       out <- stringr::str_c(out, x)