hi,
I read something about stuct and class, it says stuct's type is value type, and class's type is reference type, a bit hard to understand to me. The below code's result both are 20, I wonder why. please let it easy to understand, thanks!

yes structs are value types and classes are Reference types here you create instance of class(Myclass()) so then you assign that instance (objectA) to new veriable of that classs you create two variable pointing to one object. But remember in this scenario you create two variable whose point to same object(Myclass) and as you said that classes are referene type soo when you change objectB.val to 20 it also change objectA.val 20;

example

MyClass objectA = new Myclass(); // objectA is variable which point to Myclass object
MyClass objectB = objectA; // here you create new variable which is also point same object

if you create variable objectB like this
Myclass objectB = new Myclass(); // it mean it create new totaly new object in heap
objectA.val = 10;// now objectA.val =10
objectB.val = 20;// now objectB.val = 20
Console.WriteLine("objectA.val = {0}", objectA.val);//10
Console.WriteLine("objectB.val = {0}", objectB.val);//20

The major difference between a struct and a class is were the allocation takes place. A struct being a value type is created on the system stack when defining it. A class on the other hand being a reference type is created on the heap.

There are several other difference like, stucts are passed to functions by value meaning a copy of struct is created and passed into a function. Classes are passed by reference. Stucts can only contain data elements meaning no functions.

Also wanted to make note that your examples above dont include any stucts.

Hi babarqb,

objectA has initialized when created, it has being assigned space on system stack, so I thought when objectB = objectA, it will copy all to objectB.
from what you said, it'll only copy its "pointer" to objectB, right?

lol, yes, I cut it. another, where the class instance created on?

no you are wrong here. when object instantiate it will create object in heap and variable which hold that object create in stack. sooo when you assign already created a variable to another variable(objectB= objectA) it mean you can't create new object in heap so you only create another variable which is point to same object. new object only create when you use ( 'new') keyword and instantiate the class. and remember classes are reference type. and in other word struct are total different then class because they are value type and they live in stack and when you assign (objectB= objectA) as struct. you make a carbon copy of objectA value and assign into objectB value it mean when you change value of objectB or objectA they not effect each other because they are hold there own value. i hope you understand and sorry for my bad english. if still have doubt ask again.

for example

int i = 20;
int j = i;
j = 22;

Console.WriteLine("value of :{0} , value of:{1}",i,j);
Result: value of: 20, value of: j 22

in other word

var obj1 = new MyClass();
obj1.name = "Sam";
var obj2 = obj1;
obj2.name = "Jhone";

Console.WriteLine("Name of obj1:{0} , Name of obj2{1}",obj1,obj2);
Result: Name of obj1:Jhone ,Name of obj2:jhone

var st1 = new MyStruct("Sam");
var st2 = st1;
st2.Name = "Jhone";
Console.WriteLine(st1.Name + " :" + st2.Name);

Result: Name of st1:Sam,Name of st2:jhone

Hi babarqb,

Your english is OK, mine is real bad. I read it again and again, and finally I got all you described. "when object instantiate it will create object in heap and variable which hold that object create in stack", that's what made me clear where am I wrong before. and your example, that's helps a lot. Thanks! ^_^

Nice to see you that you have no doubt know. Good luck in future and feel free to ask every time you stuck. Happy Coding