我的while循环中的条件似乎不正确吗？

Question

trying to write a program that casts a die 3 times and once you get 3 6s in a row it prints out how many tries it took. having a problem at the end of the code, the diff between || and &&, seems like it's the opposite, have a look...

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package javaapplication12;
import java.util.*;

public class JavaApplication12 {
public static void main(String[] args) {
  Random rand = new Random();
  // this should try to cast a die 3 times and keep doing that until we get 3 6s in a row and counter 
  // how many tries it takes to get that.
  int array[] = new int[3]; // creating 3 places for castin our die 3 times in a row
  int counter1 = 0; // creating a counter to track each time we try to cast 3 die ( 3 cast = 1 try)
  do{

      counter1++; 
      System.out.println("try " + counter1); // prints out counter in the beginning of every try.

      for (int counter = 0; counter < array.length; counter++ ){
          array[counter]=(rand.nextInt(6)+1);  // a loop that fills the array with random numbers from 1-6
      }
      for(int x: array)
          {System.out.println(x);} // this is for our own to check if we have 3 6s in a row,
                                   // prints out all the numbers in out array
  }

  //so this is the I'veusing part, i've written 3 scenarios that can be written for the condtion in our
  // do- while loop...

  while (array[0]+array[1]+array[2] != 18); // this works just fine.

  while (array[0] !=6 || array[1] != 6 || array[2] != 6); // imo this should not work but surprisingly it does

  while (array[0] !=6 && array[1] != 6 && array[2] != 6); // this should work, but it doesnt.


  } 
}

Answer 1

I believe your confusion comes forth from De Morgan's laws of negation . Basically, when you have a negation of a group of conditions, you should change && by || and vice versa when you negate the individual conditions.

Or simply put:

!(A && B) == !A || !B
!(A || B) == !A && !B

In you case, you want to do this:

!(array[0] == 6 && array[1] == 6 && array[2] == 6)

aka. "while it's not true that the first is 6 AND the second is 6 AND the third is six"

Due to the above law, in order to bring the ! inside, you need to change && for || , resulting in

!(array[0] == 6) || !(array[1] == 6) || !(array[2] == 6)

Simplified to

array[0] != 6 || array[1] != 6 || array[2] != 6

Answer 2

Your first condition is: The sum is not 18, so indeed it should work correctly.

The second condition is: At least one die is not 6, so it should also work correctly.

Your last condition: No die is 6, so it will break even if a single die rolls 6, so it makes sense that it does not work.

UPDATE: The AND (&&) means that both sides of the arguments must be true for the output to be true, the OR (||) means that one side of the arguments needs to be true for the outcome to be true.

You need to revisit the basic operations of boolean algebra .

Answer 3

That is how it was supposed to work. This one:

do{
}while(array[0] !=6 && array[1] != 6 && array[2] != 6)

mean that as long as the condition is true the loop will continue. Putting it the other way - if either part is evaluated to false then the loop will stop. So if array[0]==6 then the loop will break.

Answer 4

 while (array[0] !=6 || array[1] != 6 || array[2] != 6);

This works fine because it means: "while one of the three attempts is not 6"

so the exit condition is: "all the die are 6"

while (array[0] !=6 && array[1] != 6 && array[2] != 6);

This doesn't works because it means: "while neither of the three attempts is 6"

so the exit condition is: "at least one die is 6"

 while (array[0]+array[1]+array[2] != 18);

This works fine because it means: "the die result sum is 18"

so the exit condition is: "all the die are 6" (because it's the only way to sum 18)

Answer 5

Generally:

do{
    something....
}while(some condition is true);

If you want to express it with the '&&' operator

do{
    something....
}
while (!(array[0] == 6 && array[1] == 6 && array[2] == 6));

meaning

  do { 
     something...
  }while(the expression every element in the array is equal to 6 is false);