Where and why use int a=new int?

Question

Just curious, what is the difference between:

int A = 100; 

and

int A = new int();   

I know new is used to allocate memory on the heap..but I really do not get the context here.

Answer 1

static void Main() {     int A = new int();     int B = default(int);     int C = 100;     Console.Read(); } 

Is compiled to

.method private hidebysig static void  Main() cil managed {   .entrypoint   // Code size       15 (0xf)   .maxstack  1   .locals init ([0] int32 A,            [1] int32 B,            [2] int32 C)   IL_0000:  nop   IL_0001:  ldc.i4.0   IL_0002:  stloc.0   IL_0003:  ldc.i4.0   IL_0004:  stloc.1   IL_0005:  ldc.i4.s   100   IL_0007:  stloc.2   IL_0008:  call       int32 [mscorlib]System.Console::Read()   IL_000d:  pop   IL_000e:  ret } // end of method Program::Main 

As you can see first one just initialize it and second one is just the same and third one initialize and set to 100. As for the IL code generated, they both get initialized in a single line.

so

int A = new int(); 

Is the same as

int A = default(int); 

Answer 2

Difference?

the latter ends with A being 0, not 100.

When?

Pretty much never. Maybe in some generated code it is simpler to use the new TypeName() syntax, but default(TypeName) would be preferred even then.

And new does not "allocate memory on the heap". It initializes an instance; that is all.