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Question by Lukas-Barbarossa · Jul 22, 2019 at 12:08 PM · programmingprogramming-basics

Are nested ifs different from &&?

Hi everyone

Not a broken code thing, more a request for a lesson in theory (I got my problem fixed)

In my match 3 experimenting I had a bit of broken code that looked like this

 //if the nextPiece matches the startPiece
             if(nextPiece.matchValue == startPiece.matchValue)
             {
                 //safety check that the piece isn't already in the list
                 if (!matches.Contains(nextPiece))
                 {
                     //add the next game piece to our list of matches
                     matches.Add(nextPiece);
                 }
                 else //the next piece isn't a match
                 {
                     //break out of the loop
                     break;
                 } 
             }

The problem was resolved by replacing the nested ifs with this line!

 if (nextPiece.matchValue == startPiece.matchValue && !matches.Contains(nextPiece))


My issue is, aren't these just the same?! I always thought they were both performing the same function, that both conditions have to be met. But my fix tells me otherwise.

Can some experience code guru explain to me the difference between a nested if and using &&? I need to get my head around this to make sure it doesn't happen again

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Best Answer

Answer by Hellium · Jul 22, 2019 at 12:47 PM

 if( A )
 {
     if( B )
     {
         // Do something
     }
 }

And

 if( A && B )
 {
     // Do something
 }

Are strictly identical. You won't notice any performance difference


HOWEVER

 if( A )
 {
     if( B )
     {
         // Do something
     }
     else
     {
         // Do something else
     }
 }

And

 if( A && B )
 {
     // Do something
 }
 else
 {
     // Do something else
 }

Are different.


In the 2nd case, Do something else will run if A OR B are false, while in the 1st case Do something else will run if A is true AND B is false. The two approaches are semantically different.

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avatar image Lukas-Barbarossa · Jul 22, 2019 at 01:09 PM 0
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Of course! It was the else! Thanks so much. Can't believe I didn't get that.

Really appreciate you taking the time, Hellium

avatar image Bunny83 Lukas-Barbarossa · Jul 23, 2019 at 02:18 AM 0
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I guess this question is answered so i'll accept this answer on your behalf

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