add switch statements exercise to control flow

Introduces a new step (02.switch-statements) that teaches switch statements
by converting letter grades to descriptions, building on the conditionals
exercise theme. Renumbers loops to 03 and for-of-iteration to 04.

Author: kentcdodds

exercises/04.control-flow/02.problem.switch-statements/README.mdx

@@ -0,0 +1,41 @@
+# Switch Statements
+
+👨‍💼 We've been using `if`/`else if` chains, but when you're checking one value
+against many possible matches, a `switch` statement is often cleaner.
+
+🐨 Open <InlineFile file="index.ts" /> and:
+
+1. Create a `description` variable to hold the feedback text
+2. Write a `switch` statement that checks the `grade` value and sets the
+   appropriate description:
+   - 'A' → "Excellent"
+   - 'B' → "Good"
+   - 'C' → "Satisfactory"
+   - 'D' → "Needs Improvement"
+   - 'F' → "Failing"
+   - Any other value → "Invalid grade"
+
+💰 Switch statement structure:
+
+```ts
+switch (value) {
+	case 'option1':
+		// do something
+		break
+	case 'option2':
+		// do something else
+		break
+	default:
+	// handle all other cases
+}
+```
+
+<callout-warning>
+	Don't forget the `break` statement after each case! Without it, execution
+	"falls through" to the next case.
+</callout-warning>
+
+📜 [MDN - switch statement](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/switch)
+
+🐨 Once you've completed the exercise, run `node index.ts` in the playground to
+test your work!

exercises/04.control-flow/02.problem.switch-statements/index.ts

@@ -0,0 +1,21 @@
+// Grade Description
+// Convert letter grades to descriptive feedback using switch
+
+const grade: string = 'B'
+
+// 🐨 Create a variable `description` of type string
+// 💰 let description: string
+
+// 🐨 Write a switch statement on `grade`:
+// - case 'A': set description to "Excellent"
+// - case 'B': set description to "Good"
+// - case 'C': set description to "Satisfactory"
+// - case 'D': set description to "Needs Improvement"
+// - case 'F': set description to "Failing"
+// - default: set description to "Invalid grade"
+// 💰 Don't forget the `break` after each case!
+
+// console.log(`Grade ${grade}: ${description}`)
+
+// 🦺 This line ensures TypeScript treats this as a module
+export {}

exercises/04.control-flow/02.problem.switch-statements/package.json

@@ -0,0 +1,8 @@
+{
+  "name": "exercises_04.control-flow_02.problem.switch-statements",
+  "type": "module",
+  "scripts": {
+    "start": "node index.ts",
+    "test": "node --test index.test.ts"
+  }
+}

exercises/04.control-flow/02.solution.switch-statements/README.mdx

@@ -0,0 +1,28 @@
+# Switch Statements
+
+👨‍💼 Nice! The `switch` statement makes it clear we're matching one value against
+several options.
+
+🦉 When to use `switch` vs `if`/`else`:
+
+- **Use `switch`** when comparing one value against multiple specific values
+- **Use `if`/`else`** when checking different conditions or ranges
+
+```ts
+// ✅ Good use of switch - matching exact values
+switch (grade) {
+	case 'A':
+		return 'Excellent'
+	// ...
+}
+
+// ✅ Good use of if/else - checking ranges
+if (score >= 90) {
+	grade = 'A'
+} else if (score >= 80) {
+	grade = 'B'
+}
+```
+
+The `switch` statement also supports "fall-through" where multiple cases can
+share the same code—but that's an advanced pattern we won't cover here.

exercises/04.control-flow/02.solution.switch-statements/index.test.ts

@@ -0,0 +1,19 @@
+import assert from 'node:assert/strict'
+import { test } from 'node:test'
+import { grade, description } from './index.ts'
+
+await test('grade should be "B"', () => {
+	assert.strictEqual(
+		grade,
+		'B',
+		'🚨 grade should be "B" - check your variable assignment',
+	)
+})
+
+await test('description should be "Good" for grade "B"', () => {
+	assert.strictEqual(
+		description,
+		'Good',
+		'🚨 description should be "Good" for grade "B" - use a switch statement to match grade to description',
+	)
+})

exercises/04.control-flow/02.solution.switch-statements/index.ts

@@ -0,0 +1,30 @@
+// Grade Description
+// Convert letter grades to descriptive feedback using switch
+
+const grade: string = 'B'
+
+let description: string
+
+switch (grade) {
+	case 'A':
+		description = 'Excellent'
+		break
+	case 'B':
+		description = 'Good'
+		break
+	case 'C':
+		description = 'Satisfactory'
+		break
+	case 'D':
+		description = 'Needs Improvement'
+		break
+	case 'F':
+		description = 'Failing'
+		break
+	default:
+		description = 'Invalid grade'
+}
+
+console.log(`Grade ${grade}: ${description}`)
+
+export { grade, description }

exercises/04.control-flow/02.solution.switch-statements/package.json

@@ -0,0 +1,8 @@
+{
+  "name": "exercises_04.control-flow_02.solution.switch-statements",
+  "type": "module",
+  "scripts": {
+    "start": "node index.ts",
+    "test": "node --test index.test.ts"
+  }
+}

…control-flow/02.problem.loops/README.mdx …control-flow/03.problem.loops/README.mdxexercises/04.control-flow/02.problem.loops/README.mdx renamed to exercises/04.control-flow/03.problem.loops/README.mdx exercises/04.control-flow/02.problem.loops/README.mdx renamed to exercises/04.control-flow/03.problem.loops/README.mdx

@@ -1,5 +1,5 @@
 {
-  "name": "exercises_04.control-flow_02.problem.loops",
+  "name": "exercises_04.control-flow_03.problem.loops",
   "type": "module",
   "scripts": {
     "start": "node index.ts",