Update dart.html.markdown

dart.html.markdown

@@ -503,15 +503,42 @@ example30() {
   }
 }
 
-// Optional Positional Parameter
+// Optional Positional Parameter:
 // parameter will be disclosed with square bracket [ ] & square bracketed parameter are optional.
 example31() {
-    findVolume(int length, int breath, [int height]) {
+    findVolume31(int length, int breath, [int height]) {
       print('length = $length, breath = $breath, height = $height');
     }
 
-    findVolume(10,20,30); //valid
+    findVolume31(10,20,30); //valid
-    findVolume(10,20); //also valid
+    findVolume31(10,20); //also valid
+}
+
+// Optional Named Parameter:
+// parameter will be disclosed with curly bracket { }
+// curly bracketed parameter are optional.
+// have to use parameter name to assign a value which separated with colan :
+// in curly bracketed parameter order does not matter
+// these type parameter help us to avoid confusion while passing value for a function which has many parameter.
+example32() {
+    findVolume32(int length, int breath, {int height}) {
+    print('length = $length, breath = $breath, height = $height');
+    }
+
+    findVolume32(10,20,height:30);//valid & we can see the parameter name is mentioned here.
+    findVolume32(10,20);//also valid
+}
+
+// Optional Default Parameter:
+// same like optional named parameter in addition we can assign default value for this parameter.
+// which means no value is passed this default value will be taken.
+example33() {
+    findVolume33(int length, int breath, {int height=10}) {
+     print('length = $length, breath = $breath, height = $height');
+    } 
+
+    findVolume33(10,20,height:30);//valid
+    findVolume33(10,20);//valid 
 }
 
 // Programs have only one entry point in the main function.
@@ -525,7 +552,7 @@ main() {
     example8, example9, example10, example11, example12, example13, example14,
     example15, example16, example17, example18, example19, example20,
     example21, example22, example23, example24, example25, example26,
-    example27, example28, example29, example30, example31
+    example27, example28, example29, example30, example31, example32, example33
     ].forEach((ef) => ef());
 }