Why can't you directly put digitalRead into digitalWrite?

[Si1ver]

I'm going through an Arduino tutorial book.
Just made a sketch for Arduino to turn on the led when the connected switch is pressed.
The code the book wrote was

void setup() {
// put your setup code here, to run once:
pinMode(4, OUTPUT);
pinMode(2,INPUT);
}

void loop() {
// put your main code here, to run repeatedly:
int button=digitalRead(2);
digitalWrite(4,button);
delay(10);
}

I tried putting digitalRead directly into digitalWrite.
like
digitalWrite(4,digitalRead(2));

The led turned on like the book's code, but led was much dimmer.
I want to know why it does that.

Also, the book says they put delay(10) to make the loop() don't run too quickly.
I took out the delay(10) and it worked fine. Does Arduino die quicker if the code inside loop too quickly?

[Blackfin]

Try using:

pinMode( 2, INPUT_PULLUP );

[Si1ver]

Blackfin:
Try using:

pinMode( 2, INPUT_PULLUP );

Wow, the led now works like you assign the digitalRead to a variable.
Why does it need an inner resistor to activate when you just use digitalRead inside a digitalWrite?
And I already had a resistor connected to the GND with the pin.

[taterking]

I can't imagine any reason why saying digitalWrite(4,digitalRead(2)); wouldn't work. I would guess there must be something else.

[LarryD]

“ And I already had a resistor connected to the GND with the pin.”

But you then need to pull the pin HIGH somehow ;).

FYI