how to know where my program is reading my int - c

Question

I am learning again after some years I stopped and I have a problem
the code is Supposed to to light a LED with changed time of lighting the LED just lighting non-stop without being off for a sec
int x = 0;
void setup()
{
pinMode(12, OUTPUT);
}
void loop()
{
x = 0;
while (x < 1000) {
digitalWrite(12, HIGH);
delay(1000 - x);
x = x + 100;
}
}

Answer 1

In the Arduino Studio there is an example sketch called "blink".
If you want to blink the built in led, use that.
If you have an external led connected to a pin, you can just replace the LED_BUILTIN macro in that example with your pin number.
Keep in mind that the reason the sketch is using a "macro" is because the pin for the built in led is different for different models of Arduino so the macro is automatically replaced with the correct pin number when you build the sketch for your specific board.
As for your code, the biggest issue is that you never turn off the led.
digitalWrite(12, LOW);
delay(1000 - x);
You need to "write low" to the pin (basically dropping pin voltage to zero) and then wait for some time before turning the led back on by writing high.
I am not sure why you added the while loop, but you probably don't need it.
The loop function already runs in a loop all the time, so if what you want is to blink the led in decreasing intervals, your code should look like this:
int x = 0;
void loop()
{
if (x < 1000) {
digitalWrite(12, HIGH);
delay(1000 - x);
digitalWrite(12, LOW);
delay(1000 - x);
x = x + 100;
} else {
x = 0;
}
}
}
Note that at some point this code will be blinking too fast for you to notice.
You may want to change the condition in if to something smaller like x < 800 so that the minimum interval is never shorter than 1/5 of a second.

Answer 2

byte x; // 100 ms units of blink speed ( 1000ms, 900ms, 800ms, ...100ms )
void loop() {
x = 10;
while (x > 0) {
digitalWrite(12, HIGH);
delay(100*x);
digitalWrite(12, LOW);
delay(100*x);
x--;
}
}
Blinking requires to switch the LED ON and OFF and to wait in both cases :)
BTW: each loop() run takes about 11 sec. That's fine if the arduino isn't supposed to do anything else in parallel.