c# - Why must local variables have initial values?

Question

Why must I initialize variables inside methods?

int test1; // Not initialized, but OK

public int Foo()
{
   int test2;                 // Not initialized

   int test3 = test1;         // OK
   int test4 = test2;         // An error
}

Answer 1

Fields are automatically initialized to the logical zero for the type; this is implicit. Variables must obey "definite assignment", so must be assigned before they can be read.

ECMA 334v4

§17.4.4 Field initialization

The initial value of a field, whether it be a static field or an instance field, is the default value (§12.2) of the field’s type. It is not possible to observe the value of a field before this default initialization has occurred, and a field is thus never "uninitialized".

and

§12. Variables

... A variable shall be definitely assigned (§12.3) before its value can be obtained. ...