Cannot implicitly convert 'bool' to 'int' - collision detection

Question

I am trying to make a simple collision detection class for a soccer game. Here is the code:

int Collision(int x1, int y1, int radius1, int x2, int y2, int radius2)  
{  
    int dx = x2 - x1;  
    int dy = y2 - y1;  
    int radii = radius1 + radius2;  
    if ((dx*dy)+(dy*dy)< radii * radii)  
    {  
        return true;  
    }  
    else  
    {  
        return false;  
    }  
}

The problem is with the code returning true or false. Visual Studio says it cannot implicitly convert bool to int, and I understand that, but how can I fix it? Thanks for any help.

Do you want it to return an int? If so, what value would you like represented? — Nathan Taylor
– Nathan Taylor, Commented Aug 21, 2010 at 6:07

Tommy · Accepted Answer · 2010-08-21 06:07:21Z

3

If you need to return a true/false variable, you should change your first line to this:

bool Collision(int x1, int y1, int radius1, int x2, int y2, int radius2) {

answered Aug 21, 2010 at 6:07

Tommy

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Comments

Darin Dimitrov · Accepted Answer · 2010-08-21 07:15:17Z

2

Define your function like this:

bool Collision(int x1, int y1, int radius1, int x2, int y2, int radius2)

Now you can return true or false. If you keep int then you need to return an integer value such as 0 and 1 but this doesn't express the function intent.

You could also shorten your code a bit:

bool Collision(int x1, int y1, int radius1, int x2, int y2, int radius2)  
{  
    int dx = x2 - x1;  
    int dy = y2 - y1;  
    int radii = radius1 + radius2;  
    return ((dx * dy) + (dy * dy) < radii * radii);
}

edited Aug 21, 2010 at 7:15

answered Aug 21, 2010 at 6:06

Darin Dimitrov

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12 Comments

Oded Over a year ago

@NeoHaxxor - simple, yes, but do you understand why it works?

Darin Dimitrov Over a year ago

Any reason for the downvote? Please leave a comment when downvoting.

TalentTuner Over a year ago

why you want to change the return type of function , you can use something like this int result = (dxdy)+(dydy)< radii * radii ? 1:0 and retrun result ;

Darin Dimitrov Over a year ago

@saurab, because when a function has to determine whether two points collide it should return a boolean value. It expresses much more clearly its intent to the consumer.

Darin Dimitrov Over a year ago

@saurabh, the code's already broken and there cannot be any consumers of this method simply because this method doesn't even compile. So I really don't understand your point.

|

Steve H · Accepted Answer · 2010-08-21 22:17:32Z

1

Don't forget to fix your algorithm. ((dx***dy**)+(dy*dy)< radii * radii) should be: ((dx***dx**)+(dy*dy)< radii * radii)

Just when you think: Whew! I fixed that int/bool thing,, you get a bunch of false positives.

answered Aug 21, 2010 at 22:17

Steve H

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