Merge pull request #14 from rosera/tastethedream-patch-12

Update ex4-3.md

ch04/ex4-3.md

@@ -1,20 +1,35 @@
-# 4.3 Returning values from Functions
+# 4.3 Using Optional Parameters
 
-# Example
+## Example 1
 
 ```dart
 void main() {
-  DateTime timeLondon  = getCurrentDateTime(0);
-  DateTime timeNewYork = getCurrentDateTime(-7);
-
-  print('London:    $timeLondon');
-  print('New York:  $timeNewYork');
+ printGreetingNamed();
+ printGreetingNamed(personName: "Rich");
+ printGreetingNamed(personName: "Mary", clientId: 001);
+}
+void printGreetingNamed({String personName = 'Stranger',
+  int clientId = 999}){
+ if (personName.contains('Stranger')) {
+  print('Employee: $clientId Stranger danger ');
+ } else {
+  print('Employee: $clientId $personName ');
+ }
 }
+```
 
-DateTime getCurrentDateTime(int hourDifference) {
-  DateTime timeNow  = DateTime.now();
-  DateTime timeDifference = timeNow.add(Duration(hours: hourDifference));
+## Example 2
 
-  return timeDifference;
+```
+void main() {
+ printGreetingPositional("Rich");
+ printGreetingPositional("Rich", "Rose");
+}
+void printGreetingPositional(String personName, [String? personSurname]){
+ print(personName);
+ if (personSurname != null){
+  print(personSurname);
+ }
 }
 ```
+