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content/ta/spring2018/cpsc220/feb13.md

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+# Lecture for February 13
+
+## Loops
+
+###Why Loops?
+
+While some check is true, repeat the work.
+
+While the cookies aren't baked, keep baking
+
+### Loop Building Process
+
+1. Identify one test that must be true when the loop is finished
+2. Use the **opposite** form of the test
+3. Within loop, make *progress* towards completion of the goal.
+
+### While syntax
+
+```java
+while (expression) {
+  // Loop body executes if expression is true
+}
+// Statements execute after expression is false
+```
+
+### Getting Input (Songs in a Playlist Psuedocode)
+
+```java
+// Ask user about first song
+while (user says play next song) {
+    // play next song
+    // ask user about next song
+}
+```
+
+### Nested Loops
+
+You can have loops inside loops
+
+```java
+int outer = 1;
+while (outer < 4) {
+  int inner = 1;
+  while (inner < 4) {
+    System.out.println(outer + ":" + inner);
+    inner++;
+  }
+  outer++;
+}
+```
+
+This code does the following
+
+```reStructuredText
+1:1
+1:2
+1:3
+2:1
+2:2
+2:3
+3:1
+3:2
+3:3
+```
+
+### Break Down the Problem
+
+Never write the entire program at once! This makes it incredibly hard to debug. Instead break it into small parts.
+
+Write one part -> debug until it works
+
+Write second part -> debug until it works
+
+This way you know which part of your code failed, instead of having everything fail.