adding second approach to the pointer arithmetic example

lectures/04_pointers/README.md

@@ -148,13 +148,16 @@ shrink dynamically in response to the demands of the application.
 
 ## 4.8 Stepping through Arrays with Pointers (Array Iterators)
 
-- The array code above that uses [] subscripting, can be equivalently rewritten to use pointers:
+- The array code above that uses [] subscripting, can be equivalently rewritten to use pointers. We can re-write it in two ways:
+
+### 4.8.1 First Approach
+
 ```cpp
 const int n = 10;
 double a[n];
 double *p;
 for ( p=a; p<a+n; ++p )
-*p = sqrt( p-a );
+    *p = sqrt( p-a );
 ```
 - The assignment: p = a; takes the address of the start of the array and assigns it to p.
 - This illustrates the important fact that the name of an array is in fact a pointer to the start of a block of
@@ -178,6 +181,23 @@ square root of this value is assigned to \*p.
 
 - play this [animation](https://jidongxiao.github.io/CSCI1200-DataStructures/animations/pointers/example_arrays_2/index.html).
 
+### 4.8.2 Second Approach
+
+The first approach uses pointer arithmetic in several places - just to demonstrate the usage of pointer arithmetic; but many students find it confusing and hard to understand. In contrast, the following approach is easier to understand, and **is the recommended way for you to use in tomorrow's lab**; use approach one only if you truly understand all the pointer arithmetics involved in approach one.
+
+```cpp
+const int n = 10;
+double a[n];
+double *p;
+p = a;
+int i;
+for ( i=0; i<n; ++i ){
+    *(p+i) = sqrt( (double(i) )
+};
+```
+
+This second approach also "nicely mimics the subscript notation used in the for loop above, which highlights that fundamentally array subscripts are just pointer arithmetic." - comments by our mentor Eleanor Olson, :smile:.
+
 ## 4.9 Sorting an Array
 
 - Arrays may be sorted using std::sort, just like vectors. Pointers are used in place of iterators. For example, if a is an array of doubles and there are n values in the array, then here’s how to sort the values in the array into increasing order: