So here's an example of someone (me) writing very bad C# code.
I'm trying to figure out the best method of storing values and replacing them with values as they become known.
Here's how I had been doing it earlier:
int
EMA_Value_Prev4,
EMA_Value_Prev3,
EMA_Value_Prev2,
EMA_Value_Prev,
EMA_Value;
EMA_Value_Prev4 = EMA_Value_Prev3;
EMA_Value_Prev3 = EMA_Value_Prev2;
EMA_Value_Prev2 = EMA_Value_Prev;
EMA_Value_Prev = EMA_Value;
EMA_Value = 0;
// In the below space, some code figures out what EMA_Value is
/* Some amazing code */
// EMA_Value now equals 245 (hypothetically).
Since then, I've used arrays to store this with for loops, like this:
int [] EMA_Value = new int [5];
for (xCount=4; xCount>1; xCount--)
{EMA_Value[xCount] = EMA_Value[xCount - 1]; }
For the way more advanced and experienced (and smarter) coder than I, what I should be doing instead that's either more efficient/elegant/process friendly?
Thanks in advance for any time or attention you give this question. :)
If the reason you're doing it that way is because you want to get the previous values in some case. You can think about using something like a Stack. .NET has a built in stack
Stack<int> stack = new Stack<int>();
stack.push(10)
int topValue = stack.pop()
Every time you get a new value, you call stack.push(newValue). If you want that the previous value, (behaving in the same way as the back button on a browser), you then use pop.
If you're using last N values for something like a runge-kutta ODE solver, than your solution with an array is as good as any other implementation
Related
Following to the question published in How expressive can we be with arrays in Z3(Py)? An example, I expressed the following formula in Z3Py:
Exists i::Integer s.t. (0<=i<|arr|) & (avg(arr)+t<arr[i])
This means: whether there is a position i::0<i<|arr| in the array whose value a[i] is greater than the average of the array avg(arr) plus a given threshold t.
The solution in Z3Py:
t = Int('t')
avg_arr = Int('avg_arr')
len_arr = Int('len_arr')
arr = Array('arr', IntSort(), IntSort())
phi_1 = And(0 <= i, i< len_arr)
phi_2 = (t+avg_arr<arr[i])
phi = Exists(i, And(phi_1, phi_2))
s = Solver()
s.add(phi)
print(s.check())
print(s.model())
Note that, (1) the formula is satisfiable and (2) each time I execute it, I get a different model. For instance, I just got: [avg_a = 0, t = 7718, len_arr = 1, arr = K(Int, 7719)].
I have three questions now:
What does arr = K(Int, 7719)] mean? Does this mean the array contains one Int element with value 7719? In that case, what does the K mean?
Of course, this implementation is wrong in the sense that the average and length values are independent from the array itself. How can I implement simple avg and len functions?
Where is the i index in the model given by the solver?
Also, in which sense would this implementation be different using sequences instead of arrays?
(1) arr = K(Int, 7719) means that it's a constant array. That is, at every location it has the value 7719. Note that this is truly "at every location," i.e., at every integer value. There's no "size" of the array in SMTLib parlance. For that, use sequences.
(2) Indeed, your average/length etc are not related at all to the array. There are ways of modeling this using quantifiers, but I'd recommend staying away from that. They are brittle, hard to code and maintain, and furthermore any interesting theorem you want to prove will get an unknown as answer.
(3) The i you declared and the i you used as the existential is completely independent of each other. (Latter is just a trick so z3 can recognize it as a value.) But I guess you removed that now.
The proper way to model such problems is using sequences. (Although, you shouldn't expect much proof performance there either.) Start here: https://microsoft.github.io/z3guide/docs/theories/Sequences/ and see how much you can push it through. Functions like avg will need a recursive definition most likely, for that you can use RecAddDefinition, for an example see: https://stackoverflow.com/a/68457868/936310
Stack-overflow works the best when you try to code these yourself and ask very specific questions about how to proceed, as opposed to overarching questions. (But you already knew that!) Best of luck..
i've been trying to make a program that takes (for example) 3 cards at random.
But i don't want my program to grab the same card twice, so that means it can't have duplicates, but i don't know how to do this with a image Array.
String[] card = {
"Aclubs.png",
"2clubs.png",
"3clubs.png",
};
PImage[] cards = new PImage [card.length];
void setup() {
size(1000,1000);
randomCards();
drawCards();
}
int randomCards() {
int i = (round(random(0,2)));
cards[i] = loadImage(card[i]);
return i;
}
void drawCards() {
for (int g = 0; g < 12000; g = g+round((displayWidth * 0.9))/12) {
image(cards[randomCards()], 25+g, 50);
}
}
Instead of using an array, use an ArrayList. Then remove the cards you use. Here's a small example:
ArrayList<String> things = new ArrayList<String>();
things.add("cat");
things.add("dog");
things.add("lizard");
while (!things.isEmpty()) {
int index = int(random(things.size()));
String thing = things.remove(index);
println(thing);
}
Of course, this isn't the only way to do it. You could use a Java Set, or you could use a data structure that holds what you've already picked, or you could store all of the options in a data structure, then shuffle it, then just chose from an index that you increment. Or you could use one of the array functions in the reference to do it.
It's hard to answer general "how do I do this" type questions. Stack Overflow is designed for more specific "I tried X, expected Y, but got Z instead" type questions. So you really should get into the habit of trying things out first. Ask yourself how you would do this in real life, then look at the reference to see if there are any classes or functions that would help with that. Break your problem down into smaller pieces. Write down how you would do this in real life, in English. Pretend you're handing those instructions to a friend. Could they follow your instructions to accomplish the goal? When you have those instructions written out, that's an algorithm that you can start thinking about implementing in code. Staring at code you've already written won't get you very far. Then when you do get stuck, you can ask a more specific question, and it'll be a lot easier to help you.
I'm trying to create a text adventure game that 7 rooms, with the information saved in files. This question IS similar to Connect Rooms Randomly in Adventure Game however the answer didn't exactly help me. I've gone about my program in a different way than that OP so I'm not sure how to use that answer to help me.
The idea is you have 7 rooms, named say A, B, C, D, E, F, and G. After the rooms are created, I need to randomly connect them to each other. Each room needs between 3 and 6 random connections. If room A is connected to B, C, and D, each of those rooms should be connected to A. This information is then saved to a file which is read later.
The code I have for this section so far is:
char *connections[7];
int j = 0;
int randomRoom;
for (j = 0; j <= randConnections; j++) {
randomRoom = rand() % 10;
if (randomRoom == randName) {
randomRoom = rand() % 10;
} else {
connections[j] = names[randomRoom];
}
randConnections is a random int between 3 and 6, defined earlier in the code. names is a string array that holds the names of the rooms, also defined earlier in my program.
I am pretty new to C (I'm mostly experienced with Java) so I can't figure it out. I should mention, this is all in one function defined as:
void createRooms(FILE *fp)
I know there are probably more efficient ways to do this, but at this point I'm just trying to get the code working and deal with efficiency later.
I've done a ton of googling and am honestly beating my head against the wall right now. Any help would be greatly appreciated. If there's any more code I should post or any other information let me know.
C-style strings can get a bit confusing. A "string" in pure C is a char array. Arrays in C are strongly related to pointers. In fact, instead of defining
char myCString[6] = "hello";
You could define
char * myCString = "hello";
In fact, in the first case, myCString used alone will just return a pointer to the first element. The [] operator is just a convenient dereference and increment operator. So &(myCString+1) becomes myCString[1]
So long story short, your "string" array in C is really an array of char* - pointers to the first element of an array of characters
You're trying to assign this to a single character, which doesn't make logical sense. If you mean for the connections to truly be strings, do like kcraigie says.
Here's some backup I found, I'm afraid there are more nuances and I'm not an expert, but that's the gist - https://en.wikibooks.org/wiki/C_Programming/Pointers_and_arrays#Pointers_and_Arrays
This may seem absurd coming from java - that's C for ya. C++'s standard library includes a string construct like what you'd be familiar with. It's a class that wraps a "raw" C array and controls access to it and manages it like Java and C# strings. Modern C++ best practices try to stay away from the raw arrays. You'll also notice that nothing stops you from calling MyCString[4000], which is just going to grab a piece of memory from the middle of nowhere and do heaven knows what. There is no bounds checking on raw arrays in C. Be careful!
I'm a c++ programmer and I'm having some issue with managed array. I'll explain what i mean. I'm using Visual Studio to code a Windows Form to handle a device.
I need to plot datas from a MCU connected to my PC thru a serial port. To save the values incoming from serial port, I'm using an array like that:
array<double, 1>^ datas = gcnew array<double, 1>(ndatas);
array<Byte, 1>^ byteDatas = gcnew array<Byte, 1>(2*ndatas);
where ndatas is the number of values of my series and byteDatas is the array where I will save the bytes that compose every value. Every value is made by 2 bytes.
After that, I will fill this array like this:
for(int i = 0; <=ndatas; ) {
if(bytes = serialPort1->BytesToRead>=2) {
datas[i] = getData(serialPort1, byteDatas, i);
}
i++;
}
The funcion getData is this one:
double getData(serialPort^ sp, array<Byte,1> data, int i) {
union Level {
char L[2];
signed short level;
} lvl;
sp->Read(data, i, 2);
for(int j = 0; j<=2; j++) {
lvl.L[j]= data[i+j];
}
return safe_cast<double>(lvl.level/100.00);
}
This function is on another .cpp file, so I had to use the variable SerialPort.
Everything goes like charm. If I try to use a MessageBox to display my datas, I can see how my array is correctly filled with the right values.
My next step to do, is to plot this data on a pictureBox using drawLine. But I really can't cause half of the values of the array datas are set to 0. For istance, if my series has 100 values, I can draw only the first values with the right amplitude. The other are represented, of course, as a horizontal line of zeroes.
To find this out, I have used a for cycle like that.
for(int i = 0; i<=datas->Length; i++) {
MessageBox::Show(Convert::ToString(datas[i]+" " + Convert::ToString(i+1));
}
just to be sure from when I will find the problem.
The strange part of this one is that, if I put the same MessageBox line of code under
datas[i] = getData(serialPort1, byteDatas, i);
I can display all of values without zeroes.
I'm stuck, and I don't know how to get rid of this problem. I hope I can find a little help to overcome this annoying issue.
I wish everything is crystal clear and I would like to thank everyone will give me a feedback.
Cheers,
Emiliano
When you do call getData, you're getting a valid value.
But BytesToRead goes down as you read data. At some point it drops below 2, and the rest of the for loop does nothing.
You might need to save where you are in the array when you run out of data, and when more serial data arrives, continue filling in the array from where you left off.
Plus, of course, right now you appear to be putting every data value into element 0 of the array, because you never increment i.
Also, you're reading each data point at index i, which means that you overwrite the second byte from the previous sample.
There's no need for safe_cast, the result of the division is already a double. And even if you needed a conversion, safe_cast isn't appropriate, since none of these data types are polymorphic.
Furthermore, your use of the union causes undefined behavior.
Finally, you're in C++. So why are you using what is probably the worst designed serial port API Microsoft ever made? This is C++. Calling Win32 APIs is easy, just #include <windows.h> and go, no p/invoke needed.
I am making a simple test application in C that is supposed to generate three dimensional dice. I am going to use OpenGL to do the actual drawing, but I cannot figure out how to actually generate the vertices. Of course, the whole point of this test was to see if my algorithm worked, but I found a major logic error that I cannot fix. Can somebody please point me to an article, website, or something that explains the concept? If not, although I would prefer to do the actual implementation myself, the C code is acceptable.
Basically, this is what I did before I forgot what I was doing for the algorithm:
void calculateVertices(int sides) {
BOOL isDone = FALSE;
int vectorsPerSide = 3;
VDVector3f *vertices = malloc((sizeof(VDVector3f) * (sides + 1)));
VDVector3f *normals = malloc((sizeof(VDVector3f) * (sides + 1)));
while (!isDone) {
// Start by positioning the first vertex.
vertices[0] = VDVector3fMake(0.0, 0.0, 1.0);
for (int index = 1; index <= sides; index ++) {
}
// Not a match, increase the number of vectors
vectorsPerSide ++;
}
}
Basically, it loops until a match is found. This sounds inefficient to me, but I had no other idea as to how to do this. The first vertex will actually be removed from the array at the end; I was going to use it to create the first side, which would have been used to properly position the others.
My main goal here is to be able to pass number (like 30) to it, and have it set the vertices automatically. I will not have protections against making one sided and two sided dice, because I have something special in mind. I will have those vertices entered elsewhere.
Thanks in advance for the help!
By the way, I have an algorithm that can normalize the completed vertex array. You don't have to bother helping with that.
I don't think this is possible to generalize this. How, for example would you make a fair 5 or 9 sided die? I don't think I have ever seen such a thing. A quick search on wikipedia suggests platonic solids may be what you are after. http://en.wikipedia.org/wiki/Platonic_solid