C++ Boolean Assignments - GameCreators Forum

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heyufool1

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Posted: 23rd Jan 2011 19:21

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Hi! I'm making a game and editor in C++ but I came across this today:

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topSpeed = mFastMove ? mTopSpeed * 20 : mTopSpeed;

I'm assuming what this really is, is:

+ Code Snippet

if ( mFastMove )
     topSpeed = mTopSpeed * 20;
else
     topSpeed = mTopSpeed;

I can't find any information on this using google so can anyone clarify this for me? Also, I rarely see this method used so is it frowned upon for any reason? Thanks!

"So hold your head up high and know, it's not the end of the road"
Impulse Game Engine

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BiggAdd

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Posted: 23rd Jan 2011 19:25 Edited at: 23rd Jan 2011 19:29

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Its called a Ternary Operation/Operator:

http://en.wikipedia.org/wiki/Ternary_operation

And yes you are right, it does the same as your code snippit.

Quote: "
I can't find any information on this using google so can anyone clarify this for me? Also, I rarely see this method used so is it frowned upon for any reason? Thanks!"

Its just used as a neater way of assigning a variable under a condition. Its perfectly valid.

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heyufool1

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Posted: 23rd Jan 2011 19:31

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Ahh, cool. Learn something everyday

thanks for the info!

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Impulse Game Engine

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Neuro Fuzzy

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Posted: 23rd Jan 2011 22:49

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I love the ternary operator!!!!

I remember, my teacher wanted us to finish this:
http://codingbat.com/prob/p183562
in the shortest number of lines. The Challenge is as follows:

+ Code Snippet

We want to make a row of bricks that is goal inches long. We have a number of small bricks (1 inch each) and big bricks (5 inches each). Return true if it is possible to make the goal by choosing from the given bricks. This is a little harder than it looks and can be done without any loops.

makeBricks(3, 1, 8) → true
makeBricks(3, 1, 9) → false
makeBricks(3, 2, 10) → true

my solution:

+ Code Snippet

public boolean makeBricks(int small, int big, int goal) 
{
  return ((((big>(goal/5))?goal/5:big)*5+small)>=goal);
}

If you use underscores for variables and ternary operators a lot, your code can be annoyingly hard to read:
(_==__?_*__:__/_)<___?_:__

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heyufool1

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Posted: 24th Jan 2011 00:45 Edited at: 24th Jan 2011 00:48

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Quote: "return ((((big>(goal/5))?goal/5:big)*5+small)>=goal);"

nice, did you start with that or did you go from a full decision structure down to that? Just curious because it's hard for me to follow

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Neuro Fuzzy

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Posted: 24th Jan 2011 05:06

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Quote: "nice, did you start with that or did you go from a full decision structure down to that? Just curious because it's hard for me to follow "

Originally I was gonna type three lines

int blocks=((big>(goal/5))?goal/5:big)*5+small
if goal<=blocks then return true;
return false

But while typing the second I realized the last two lines are redundant. It's checking if a boolean is true or false and returning a boolean, when you could just return that boolean >.>
Basically, the first ternary returns the largest number of "big bricks" that can fit into "goal". If there are more bigBricks than can fit into Goal, then goal/5 rounded down will be the number of bigBricks (integer division rounds down). That number times five is the length in inches, and since small bricks are the smallest resolution, if this number plus the length of the small bricks is greater or equal to the total length, we can fit everything together.

The ternary operator can make simple logic look complicated, BUT also more compact and neat. Generally, if I have to nest more than two or three ternary statements, I just nest else/ifs.

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