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Everything posted by C30N9

In an assignment, I created a simple memory game.
Memory Game.
Also, I have a question. Which is better to use to close the program? System.exit(0)? Or dispose() to destroy the window, which already terminates the program on close? 
Here is a code for a calculator using GUI and event driven programming. One annoying problem is that the numbered buttons call the action method twice. Suggestions to improve the program is much appreciated.
EDIT: An error found. Putting 0s in front of numbers might manipulate the calculation a bit.
code:
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Regarding the registering each action twice, that's because you're just listening for all events without filtering them out by type (e.g. button pressed, button released, etc.), and even buttons can generate many kinds of events, not just "pressed". Whenever you click on a button, you generate at least a "button pressed" and "button released" event, while I think there's also a "button clicked" event which only triggers upon a complete pressrelease cycle.


I've been asked to write a method which is public static Object max(Object[] a). It should return the highest Object in an Object array using compareTo method. However, with this method's parameter, since Object doesn't have compareTo method, I'm supposed to put several if statements to determine if the object is an instanceof Account, or Employee, or other classes that use compareTo:
So I changed the function to this:code:
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Which works fine, and I think it's similar to java.util.Arrays.max(anArray). But I heard that it's not a very good idea to do that. Is it healthy to do this?code:
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I'm supposed to write a method that acts like java.lang.String.split, except that this new method returns a String array including the delimeters. For example:
split("Java#HTML#Cpp", "#") would return "Java", "#", "HTML", "#" and "Cpp" in an array. I already done the hard part, which returns the array correctly. However, I don't how to make it work with regular expressions, such as:
split("Java#HTML$Cpp%Python", "[#$%]"). It should return:
"Java", "#", "HTML", "$", "Cpp", "%", "Python".
Any ideas?
Here is my code BTW:code:
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fraggle said:
Assuming the assignment requires the second argument to be a regexp, if I was running the class you'd get a fail mark. What you have implemented is not a regexp.
This problem is put very early in the book, probably a mistake, as it didn't discuss regular expressions at all in the chapter. My instructor limited me to making this, not an actual regex. I kept the method naming the same though, that's why I didn't understand "regex" at first.

So I want the output to be this:
____5 (four spaces)
___45 (three spaces)
__345 (and so on...)
_2345
12345
Using without more than 2 loops. Doesn't matter any language, but C or Java works. 
Yesterday, in my C programming lab, I was solving problems with recursions, the hardest part was that some of them required using variables inside recursive functions for better solutions. I tried to avoid declaring variables inside them as that would harm the memory, so I ended up declaring global variables, which ended in a mess. Here is an example of my functions:
The number "10" in the above code is the size of the array I declared later in the main function. I could use a constant value of 10 in SIZE, but a better way is to put another integer variable in the function to store length value like the comment I wrote, but this will make it change its value to the new length, and it will keep declaring integer type variable.code:
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This messy function is supposed to check if a string is a palindrom string. length's value is the length of the character array "LeooeL", same issue as the first code (putting the length as a variable). z (didn't bother to pick a name for it) should be used to indicate whenever it should stop checking, but I didn't finish the function, so I put a comment for each statement concerning it, as it's the not the issue here. Notice where I declared the variables, not favorable.code:
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C30N9, that extra else if clause you inserted isn't necessary. The && logical operator is shortcircuiting in C, meaning that if the left side evaluates to false, the right side recursive call will not be executed, and the result will be 0, which will be returned.

Jonathan said:
C30N9, that extra else if clause you inserted isn't necessary. The && logical operator is shortcircuiting in C, meaning that if the left side evaluates to false, the right side recursive call will not be executed, and the result will be 0, which will be returned.
And even if C didn't have shortcircuiting, the c[0] == c[len  1] part in the third return statement would be redundant.
Actually you can simplify further to just:
code:
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EDIT: Nevermind, I misunderstood it at first. I thought that when I add "6", it would add to array[5] (or the sixth element of the array). Problem solved.
This is for an assignment. I'm not asking for the solution, but I'm a bit confused:
Write a C program to create and manipulate a one dimensional array (list) of up to a hundred sorted (ascending order) numbers by using functions to insert, remove, or print elements as follows:
 Function insert: will search for the appropriate position of a given element and if the element is already in the list will display an error message. If not, the function will shift all the elements starting from the position of the element to the right of the array and then insert the element into that position.
 Function remove: will search for the element to be removed and if not found will display an error message. If the element exists, the function will remove it and shift all the elements that follow it to the left of the array.
 Function print: will print the elements that exist in the array at that point.
Your program should display a menu to the user that allows him/her to insert, remove, or print as many elements as they want until they want to stop. If an element is inserted into an already full list, an error message should be displayed. The array (list) at the beginning should be empty.
Example of a sample run:
Enter your choice: 1) insert 2) remove 3) print 4) exit
2
List is empty, No change
Enter your choice: 1) insert 2) remove 3) print 4) exit
1
Enter element to insert
6
Element 6 is inserted
Enter your choice: 1) insert 2) remove 3) print 4) exit
1
Enter element to insert
9
Element 9 is inserted
Enter your choice: 1) insert 2) remove 3) print 4) exit
1
Enter element to insert
7
Element 7 is inserted
Enter your choice: 1) insert 2) remove 3) print 4) exit
2
Enter element to remove
112
Element 112 does not exist, No change
Enter your choice: 1) insert 2) remove 3) print 4) exit
2
Enter element to remove
6
Element 6 is removed
Enter your choice: 1) insert 2) remove 3) print 4) exit
3
Elements in list are:
7
9
Enter your choice: 1) insert 2) remove 3) print 4) exit
1
Enter element to insert
7
Element 7 already exists, No change
Enter your choice: 1) insert 2) remove 3) print 4) exit
4
Goodbye
It seems to me that the example is wrong, shouldn't element 7 become 6? And what if the 100th element (99) is shifted to the right? They didn't say anything about the limits. 
Today, in my Calc II exam, I've came across the question of finding the derivative of an inverse function when x = 2. The function was as I remember:
f(x) = e ^ 2x + 4x + 1
I didn't know how to solve for x algebraically after I substituted f(x) with 2 (or using ln or exp functions). So I put automatically x = 0 as it will satisfy the equation and then I proceeded. Luckily, it was a multiple choice question, so the method of solving isn't important.
How do I solve this? Show previous comments 4 more

Somehow I doubt that's how they expected you to solve it. Unless they actually teach kids the Lambert W function in Calc II nowadays? There's probably some simpler trick I'm not aware of, been ages since I touched this stuff.code:
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You don't really need to know about the Lambert W function unless you're solving a more general version of the problem. Here you just need the inverse at one specific value, y = 2, and since it's an exam problem, this point was naturally chosen so that the input x = 0 can be found by just inspecting the equation.
This is a typical feature of exam problems, less common in real world problems.

This code is supposed to calculate e to the power x. It works fine at lower numbers, but then at x = 3.6, the output starts to decrease as x goes up. What's wrong?
C language.
EDIT: The problem was that "factorial" function was an int, so at high values, it won't work.
code:
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I'm majoring in computer science (first year), and I'm thinking of taking minor in math. The reason is because of its connection to computer science (since it's a subfield of math), and I like it a lot. The question is, are these a good pair?
For CS degrees, math courses include Calculus I and II, Discrete Mathematics, Statistics, Linear Algebra and Numerical Methods. As for the mathematics minor, it includes Calculus III, Foundations of Mathematics, Normal Differential Equations, Mathematical Analysis I, Abstract Algebra I and other math courses in the choice of the student.
I feel getting a minor in math is a waste of time. It's because where I live, computer scientists and engineers usually end up in programming jobs, or maintaining computers. So it's very likely that I won't work in the "theoretical" part of computer science, and I "assume" that math is applied more on the theoretical part than programming (or software engineering).
Shall I forget it and pursue other minors, or am I being ignorant about how good it is to study such pair?
Pretty much all oldschool CS profs I know started out as Math majors, with a specialization in CS acquired on top of that. That was before most universities introduced a separate/more technical CS curriculum, as well as the various "computer engineering" ones.
So the two are definitively compatible, but the only reason for pursuing them together today would be if you're interested in an academic career or working in a specialized field such as cryptoanalysis or numerical computing (which usually point to an academic/research career anyway). 
When I was a CompSci major, I was required to minor in math (with a 2nd minor of my own choice; I chose Japanese). At first it didn't seem necessary, but as I got into tougher classes, such as Computer Security, I saw the reason. Unfortunately I can't math to save my life, and thus I switched to a BA in Applied Computing, which didn't require the math.
However, the "BS in Computer Science" they offered didn't actually cover the things I'd need to be a programmer inthelarge. They said it did, but not really. They instead expected people in the BS program to think about things in a more academic way, then go off to do research or something. Sure, you learned some good programming skills (C/C++, C#, some basic x86 assembly in Intel syntax, Prolog, and how to construct certain data structures like lists and queues), but their focus was more on making you a computer scientist. This is why I switched to the BA, which was more along the lines of "we're teaching you to be a programmer". But that was my specific school, which didn't exactly have a stellar CompSci department.
On the other hand, a good foundation in at least some of the science underlying programming is good to know. Plus, certain fields will require you to know some of the higher maths. 3d programming and linear algebra comes to mind.
Disclaimer: I never finished college.


I'm currently majoring in Computer Science, but it is possible to switch to Computer Systems Engineering. In general, CS should focus more on math, theories and softwarerelated stuff than CSE, but after looking through my university's guide for BA degree, it seems that CS is a bit "contained" in CSE. For example, CSE students take several courses that are essential to get into software engineering (programming, data structure and management, and software engineering courses), with another courses related to Electrical Engineering and hardware stuff, but some share the same name of other CS courses (AI, Operating Systems, Algorithms). Plus CSE students can take some courses in CS as elective courses.
You have to be good in Physics and Mathematics to switch or to do well, which I am good at both. I just keep feeling that I'm wasting a chance to study engineering and become good at both software and hardware rather than only focusing on Computer Science. At the end of the day, either degrees will likely get me the same job, but an engineer is usually generally known as being smarter (because he is an "engineer", plus the requirements to get engineering are harder than the ones to get into CS).
Should I stop listening to people who keep telling me that I've took the wrong choice choosing CS over CSE even though I can make it through in the latter major? 
I have a form in html, but I don't know to make it perfectly aligned. I tried putting it in a table with two columns, but I still have problems:

A twocolumn table will not allow you to line everything up nicely. Try something like this: http://www.dvdflick.net/storage/form.html

Styles aren't applied to the text. Why?
code:
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Presumably the nested <<b></b>h<b></b>2> (etc.) and <<b></b>p> tags are the problem. It's probably forceclosing the <<b></b>p> tags in those cases, and thus losing the style information.
<<b></b>h1> (etc.) tags are kind of like beefedup <<b></b>p> tags and shouldn't be nested with them.
Also, you need to use straight quotes instead of angled ones. I've fixed these issues and pasted it below. Actually, I'm not sure which was the problem; maybe both were. Don't have time to check further at this point.


1 A car, initially going eastward, rounds a 90 degrees curve and ends up heading southward. If the speedometer reading remains constant, what's the direction of the car's average acceleration vector?
2 A plane with airspeed 370 km/h flies perpendicularly across the jet stream, its nose pointed into the jet stream at 32 degree from the perpendicular direction of its flight. Find the speed of the jet stream.
3 An object undergoes acceleration 2.3i + 3.6j m/s^2 for 10 s. At the end of this time, its velocity is 33i + 15j m/s. What was its velocity at the beginning of the 10 s interval? By how much did its speed change? By how much did its direction change? Show that the speed change is not given by the magnitude of the acceleration multiplied by the time. Why not?
4 A particle leaves the origin with initial velocity v0 = 11i + 14j m/s, undergoing constant acceleration a = 1.2i + 0.26j m/s^2. When does the particle cross the yaxis? What's its ycoordinate at the time? How fast is it moving, and in what direction?
5 A jet is diving vertically downward at 1200 km/h. If the pilot can withstand a maximum acceleration of 5g before losing consciousness, at what height must the plane start a quarter turn to pull out of the dive? Assume the speed remains constant. Show previous comments 5 more

In Russia the government actually pays for your education if you do well enough on the entrance exams, so I don't need to pay anything hehe. I guess this is one of the cool things about my country. I was very lucky btw, got the total of 270 out of 300 (90 math, 92 informatics, 88 russian language) on the tests, which was the minimal total mark required to get free education on this speciality.

So much "free" time (12 hours) that I hate to sit lonely in public, so I went/hid in the library which is a very friendly environment for spending time yourself. This is gonna be boring if I'm going to do this everyday.

You gotta find out where the party's at. To do that, you need to talk to some cute girls in your classes. "Excuse me, do you know where the ___ Hall is?" or.. "How are you liking your classes so far?" Or any other thing you need information about. Whenever you have a question, consider it a golden opportunity to ask a cute girl for the answer. You can stop random girls on your way to class, or sit next to girls in your classes and ask them before class starts. Don't blow those opportunities on professors or .. um, dudes. Of course making guy friends is also a good way to find out where the party is at, tho.
Good luck, and make the most of it. Best four years of your life has just begun. Don't waste them! (And when I say don't waste them, I mean, don't spend the entire time being responsible and studying).


?
Also how is doubling time calculated in general. Show previous comments 7 more

let me try...

1/x < 2
we can see that 1/x = 2 when x = 1/2, and that increasing x will decrease 1/x, so the answer is
x > 1/2 I guess
or maybe you can just multiply both parts by x and then divide by 2, but dunno if you're allowed to do that??? maybe it will get tricky since x might be either positive or negative, dunno

classic method here, multiply numerator and denominator by something so you can use the formula (xy)*(x+y)=x^2  y^2
lim x→∞ (x − √ (x^2 + x − 1)) = lim x→∞ ((x^2  x^2  x + 1) / (x + √ (x^2 + x  1)) = lim x→∞ ((1  x) / (x + √ (x^2 + x − 1))) = lim x→∞ ((1 + 1/x) / (1 + √ (1 + 1/x  1/x^2))) = 1 / (1 + 1) = 1/2.

x^3  x  1 = 0
no idea, either I'm missing something trivial or you just have to take a lucky guess? 
Memfis said:
let me try...

1/x < 2
we can see that 1/x = 2 when x = 1/2, and that increasing x will decrease 1/x, so the answer is
x > 1/2 I guess
or maybe you can just multiply both parts by x and then divide by 2, but dunno if you're allowed to do that??? maybe it will get tricky since x might be either positive or negative, dunno

I actually solved this before (x < 0 or x > 1/2), but I wanted to double check.
x^3  x  1 = 0
no idea, either I'm missing something trivial or you just have to take a lucky guess?
There is no "regular" way to solve this, instead there is the cubic general formula.