what is format to make digitalWrite variable?

Projects Programming
3

digitalWrite(i, HIGH);

Or make led an array. Use [ ]

byte led[ ] = {10, 11, 12, 13,};

for (i=0; i<4; i=i+1){
pinMode (led[i], OUTPUT);
}

and then 

for (i=0;i<4;i++)
  {
    digitalWrite(led[i], HIGH);   // turn the LED on
    delay(10);               // wait for a second
    digitalWrite(led[i], LOW);
    delay(10);
  }

Some names are system names and cannot be used. led might be one of them.
try ledPin[ ] if you see some error statements about that.