Arduino Uno: How would I input a priority encoder?

Chagrin:
See Arduino Playground - BitMath

void loop() {

val = 0;  // initialize to zero

if( digitalRead(onepin)== HIGH)
   val &= B00000001;
 if (digitalRead(twopin) == HIGH)
   val &= B00000010;
 if (digitalRead(fourpin) == HIGH)
   val &= B00000100;

delay(100);

Serial.println(val);
}

That seems to be clearing the other bits rather than setting the bit you wanted. In any case I'd suggest putting the pin numbers in an array and using a for loop to read from each pin and write the result to the corresponding bit using bitWrite().