objective-c – 查找点靠近直线和直线端点之间

-(Boolean)isOnLine:(Line*) line point:(CGPoint) point{
    //If between two dots:
    if (((line.first.x <= point.x && point.x <= line.last.X)||(line.first.x >= point.x && point.x >= line.last.X))&&((line.first.y<=point.y && point.y<= line.last.y)||(line.first.y>=point.y && point.y>=line.last.y)) ) {    
        //Calculate distance:
        double dist = (((doublE)point.y - line.first.y)) / (0.00001+((doublE)(point.x - line.first.X)))- ((doublE)(line.last.y - line.first.y)) / (0.00001+((doublE)(line.last.x - line.first.X)));
        NSLog(@"Dist to line: %f",fabs(dist));
        return fabs(dist) <0.5;
    }else
        return NO;  
    }
}

然而,不知何故,该功能不适用于垂直线.我的猜测是if子句在某种意义上是无效的.