From 42e79c31dc1ce7c83b6bbd525e84e463aa4d9643 Mon Sep 17 00:00:00 2001
From: Perry Kivolowitz <perry@kivolowitz.com>
Date: Tue, 7 Jun 2022 15:17:55 -0500
Subject: [PATCH] added more explication and questions

---
 section_1/while/README.md | 70 +++++++++++++++++++++++++++++++++++++--
 1 file changed, 67 insertions(+), 3 deletions(-)

diff --git a/section_1/while/README.md b/section_1/while/README.md
index 6a1d995..97a8730 100644
--- a/section_1/while/README.md
+++ b/section_1/while/README.md
@@ -10,11 +10,19 @@ To illustrate this, here is a flow chart of an `if` statement (on the left) comp
 
 The closing brace in an `if` statement is indicated by the red arrow head. This isn't a branch, the code flow simply falls through to the statement beyond the closing brace. In the `while` loop, the behavior of the closing brace changes to be that of a branch back to just before the evaluation of the boolean condition (the "Decision").
 
-A new label is placed before evaluating the "Decision". 
+A new label is placed before evaluating the "Decision".
 
 A new unconditional branch is placed after the end of the "Code Block."
 
-For review, here is the assembly language for an `if` statement:
+For review, consider this C or C++ code:
+
+```c
+if (a >= b) {
+	// CODE BLOCK
+}
+```
+
+here is the assembly language for this `if` statement:
 
 ```asm
     // Assume value of a is in x0                                       // 1 
@@ -25,7 +33,15 @@ For review, here is the assembly language for an `if` statement:
 1:                                                                      // 6 
 ```
 
-Here is the code for the `while` showing one new label and one new unconditional branch:
+Now, consider this `while` loop:
+
+```c
+while (a >= b) {
+	// CODE BLOCK
+}
+```
+
+Here is the code for the `while` showing the addition of one new label and one new unconditional branch:
 
 ```asm
     // Assume value of a is in x0                                       // 1 
@@ -40,3 +56,51 @@ Here is the code for the `while` showing one new label and one new unconditional
 ```
 
 Temporary label `2` on `line 9` takes the place of the line after the closing brace in a `while` loop.
+
+Temporary label `1` on `line 4` is the end point of the red arrow in the right hand
+flow chart above.
+
+## Summary
+
+A `while` loop is an extension of the `if` statement. A simple `if` contains one conditional branch and one label.
+
+A `while` loop contains at least two labels, one conditional branch and one unconditional branch. We acknowledge the possibility that the unconditional branch could be made a conditional one, but this is rarely done in assembly language and impossible in higher level languages like C and C++ since the branch is simply the closing `}`.
+
+## Questions
+
+### 1
+
+(T | F) This code has a problem:
+
+```asm
+    // Assume value of a is in x0                                       // 1 
+    // Assume value of b is in x1                                       // 2 
+                                                                        // 3 
+ 1: cmp     x0, x1                                                      // 4 
+    b       2f                                                          // 5 
+    // CODE BLOCK                                                       // 6 
+    b       1b                                                          // 7 
+                                                                        // 8 
+2:                                                                      // 9 
+```
+
+Answer: True - the unconditional branch on `line 5` doesn't reference the
+results of the `cmp` that comes before it. The `CODE BLOCK` will never be
+executed.
+
+### 2
+
+(T | F) This attempt at a `while` loop has a problem:
+
+```asm
+    // Assume value of a is in x0                                       // 1 
+    // Assume value of b is in x1                                       // 2 
+                                                                        // 3 
+ 1: cmp     x0, x1                                                      // 4 
+    ble     2f                                                          // 5 
+    // CODE BLOCK                                                       // 6 
+                                                                        // 7 
+2:                                                                      // 8 
+```
+
+Answer: True - missing a branch back to label `1`, there is no loop.