Question

Without initialization how is it possible to assign values to arrays?

string[] s={"all","in","all"};

I mean why did not the compile show error?.Normally we need to 
initialize ,before assign values.

Answer 1

It’s just syntactic sugar.

This:

string[] s = {"all","in","all"};

is compiled to the same code as:

string[] tmp = new string[3];
tmp[0] = "all";
tmp[1] = "in";
tmp[2] = "all";
string[] s = tmp;

Note that the array reference is not assigned to s until all the elements have been assigned. That isn’t important in this particular case where we’re declaring a new variable, but it would make a different in this situation:

string[] s = { "first", "second" };
s = new string[] { s[1], s[0] };

The same is true for object and collection initializers – the variable is only assigned at the end.