1）Learning diary for flutter about dark

I'v bean learning about Flutter these days. There are many problems in the process of learning.For example，The Dart SDK un available Because the computer system reinstalled yesterday.

So before I  start learning today，I have to reinstall Dart SDK for a long time. 

Use this time to review Dart's grammar.

OK, Let's review now. 

First of all,I'll write a smiple Dart program

Like many programming languages, Dart includes classes and functions and various type of data

My program will use them

void main()=>myEnter();
void myEnter(){
  print(sum(3,2,4));
  new A().fun();
}
num sum(int d,e,double f ,{int a=1,var b:3,double c=2.2}){
  return a+b+c+d+e+f;
}
class A{
  var a;
  A(){
    a='hello world';
  }
  fun(){
    print(a);
  }
}

1)When there is only one line in the method ,you can use => to shorthand.

2)Method may not have to be in a class.

3)Parameters can be  undeclared，written in brackets must use equal sign to specify the default value