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Thread: comparing values in a boolean array

  1. #1
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    Default comparing values in a boolean array

    Hi,

    I am trying to figure out how compare two values in a boolean array. For example:

    if [i] = true, compare [i+1] and [i-1]... then, if one is true, and the other is false, [i] = true.

    Here's a snippet of what I am working on:

    public static void theLivingDead(boolean[] villagers) {

    for (int i=0; i<villagers.length; i++) {
    if (villagers[i] == true) {
    if (villagers[i++] == true && villagers[i--] == false) {
    villagers[i] = false;
    }
    else {
    villagers[i] = true;
    }
    }
    else {
    if (villagers[i++] == true && villagers[i--] == false) {
    villagers[i] = true;
    }
    else {
    villagers[i] = false;
    }
    }

    }
    }

    You can probably see what I am trying to do by reading the code, however, I am clearly missing something.

  2. #2
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    Default Boolean array comparison/arguments

    Hi,

    I am trying to figure out how compare two values in a boolean array. For example:

    if [i] = true, compare [i+1] and [i-1]... then, if one is true, and the other is false, [i] = true.

    Here's a snippet of what I am working on:

    public static void theLivingDead(boolean[] villagers) {
     
          for (int i=0; i<villagers.length; i++) {
                if (villagers[i] == true) {
                    if (villagers[i++] == true && villagers[i--] == false) {
                        villagers[i] = false;
                    }
                   else {
                        villagers[i] = true;
                   }
         }
         else {
              if (villagers[i++] == true && villagers[i--] == false) {
                  villagers[i] = true;
              }
              else {
                  villagers[i] = false;
              }
         }
     
    }
    }

    You can probably see what I am trying to do by reading the code, however, I am clearly missing something.

  3. #3
    Super Moderator Norm's Avatar
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    Default Re: Boolean array comparison/arguments

    how compare two values in a boolean array
    You can use the == operator to compare two boolean values:
       if(theArray[i] == theArray[idx2])  { // compare two values in an array

    Note: you do not need to use == true to test a boolean variable. The variable's contents can be used directly:
       if(boolVal == true) // poor technique
     
       if( boolVal)   // better to use directly
    An if statement takes a boolean expression and a boolean variable works there.
    If you don't understand my answer, don't ignore it, ask a question.

  4. #4
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    Default Re: Boolean array comparison/arguments

    in
    if(theArray[i] == theArray[idx2])  { // compare two values in an array

    'idx2' would be a seperate index, correct?

    I am trying to compare three 'side by side' values..

    say for instance, [3] = true, I want to see whether or not [2] is true/false, and also whether or not [4] is true/false ((((within the same array)))).... and be able to keep, or alter the value of [3]....

  5. #5
    Super Moderator Norm's Avatar
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    Default Re: comparing values in a boolean array

    compare three 'side by side' values.
    There are only two operands in any comparison.
    With three different binary values there can be 8 different combinations: T,T,T to F,F,F
    Which of those 8 combinations do you want to test for?


    'idx2' would be a seperate index, correct?

    I am trying to compare three 'side by side' values..
    idx could be i+1
    If you don't understand my answer, don't ignore it, ask a question.

  6. #6
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    Default Re: comparing values in a boolean array

    I'm not sure now, honestly, though I believe I would want to test all of them. This is how the algorithm reads:

    if the current villager is alive:
    * if only one neighbor is alive, the current villager is dead in the next generation.
    * otherwise,the current villager is alive in the next generation.
    *
    otherwise (the current villager is dead):
    * if only one neighbor is alive, the current villager is alive in the next generation.
    * otherwise, the current villager is dead in the next generation.
    *

  7. #7
    Super Moderator Norm's Avatar
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    Default Re: comparing values in a boolean array

    I would want to test all of them
    Ok, that could be 8 if statements, one for each case.
    For example to test boolArray's contents for
    case 1: all true:
    if(boolArray[i] && boolArray[i+1] && boolArray[i+2])
    and case 8: all false:
    if(!boolArray[i] && !boolArray[i+1] && !boolArray[i+2])
    If you don't understand my answer, don't ignore it, ask a question.

  8. #8
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    Default Re: comparing values in a boolean array

    I have managed to see a positive change within the last few moments of your time, Norm, Thank you! Although I have managed to breach a wall, thanks to you, I believe now I have quite a-ways to get yet. Here's what my code looks like now:

     for (int i=0; i<villagers.length; i++) {
    		 	 	 if (villagers[i]) {
    		 	 	 	 if (villagers[i+1] && !villagers[i-1]) {
    		 	 	 	 	 villagers[i] = false;
    		 	 	 	 }
    		 	 	 	 else {
    		 	 	 	 	 villagers[i] = true;
    		 	 	 	 }
    		 	 	 }
    		 	 	 else {
    		 	 	 	 if (villagers[i+1] && !villagers[i-1]) {
    		 	 	 	 	 villagers[i] = true;
    		 	 	 	 }
    		 	 	 	 else {
    		 	 	 	 	 villagers[i] = false;
    		 	 	 	 }
    		 	 	 }

    I will provide tests for the different combinations, and report back. Thanks again for the help!

  9. #9
    Super Moderator Norm's Avatar
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    Default Re: comparing values in a boolean array

    Ok, I'm glad you are making progress.
    If you don't understand my answer, don't ignore it, ask a question.

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