Update day01(Variables)

Author: MabelJay

day01(Variables)

@@ -57,4 +57,14 @@ summary:
 
    String Operator:
    •Definition: When the ‘+’ is used on strings the ‘+’ operator is called the concatenation operator.
+   
+   9. type conversion:
+      parseInt();          //return a number only include integral part. 
+      parseFloat();        //return a floating point number
+      Number();            //return a number(maybe integral number and float point number)
+      .toString(); String();   //return a string
+      Boolean();              //return a boolean value
+      
+      
+