I have the following code:
int countLatticePoints(const double radius, const int dimension) {
static std::vector<int> point {};
static int R = static_cast<int>(std::floor(radius));
static int latticePointCount = 0;
for(int i = -R; i <= R; i++) {
point.push_back(i);
if(point.size() == dimension) {
if(PointIsWithinSphere(point,R)) latticePointCount++;
} else {
countLatticePoints(R, dimension);
}
point.pop_back();
}
return latticePointCount;
}
When I make the call countLatticePoints(2.05, 3) I get the result 13 which is correct. Now I change the parameters and then call countLatticePoints(25.5, 1) I get 51 which is also correct.
Now when I call countLatticePoints(2.05, 3) and countLatticePoints(25.5, 1) right after each other in the main program I get 13 and then 18 (instead of 51), I really don't understand what i'm doing wrong ? When I call each one individually without the other I get the correct result but when I call the functions together one after the other my results change.
You're misusing static.
The second time you call the function, you push additional values into point.
Edit: I hadn't spotted the recursion. that makes things more complex, but static is still the wrong answer.
I'd create a 'state' object, and split the function into two. One that recurses, and takes a reference to the 'state' object, and a second one which initialises the state object and calls the first.
struct RecurState
{
std::vector<int> point;
int latticePointCount
RecurState() : latticePointCount(0)
{
}
}
Outer function:
int countLatticePoints(const double radius, const int dimension)
{
RecurState state;
return countLatticeRecurse(radius, dimension, state)
}
Recursive function
int countLatticeRecurse(const double radius, const int dimension, RecurseState &state)
{
...
}
Local, static variables only get initialized once, on the first function call.
Related
I want to be able to pass a struct member into a function:
struct threeBuckets {
int bucketA;
int bucketB;
int bucketC;
};
threeBuckets allCombinations[512000] = {{0,0,0}};
int totalCombinations = 1;
int counter = 0;
//note that pourer, receiver, and other are one of the struct members (bucketA, bucketB, and bucketC)
void pour(pourer, receiver, int receiverCap, other) {
int finalTriple[3];
allCombinations[totalCombinations].bucketA = allCombinations[counter].bucketA;
allCombinations[totalCombinations].bucketB = allCombinations[counter].bucketB;
allCombinations[totalCombinations].bucketC = allCombinations[counter].bucketC;
allCombinations[totalCombinations].receiver = allCombinations[totalCombinations].receiver + allCombinations[counter].pourer;
allCombinations[totalCombinations].pourer = 0;
if (allCombinations[totalCombinations].receiver > receiverCap) {
allCombinations[totalCombinations].pourer = allCombinations[totalCombinations].pourer + allCombinations[totalCombinations].receiver - receiverCap;
allCombinations[totalCombinations].receiver = receiverCap;
}
finalTriple[0] = allCombinations[totalCombinations].bucketA;
finalTriple[1] = allCombinations[totalCombinations].bucketB;
finalTriple[2] = allCombinations[totalCombinations].bucketC;
//some more irrelevant code
}
As I've hopefully made clear, the parameters pourer, receiver, and other are bucketA, bucketB, and bucketC (in no particular order, the order does change depending on when I call the function.) There are several places where I want to modify the instance
allCombinations[totalCombinations].pourer
for example. How do I use the struct member as a parameter, and what type do I use to specify it?
Note: I'm mostly a beginner and am new to StackOverflow, so if anything else I'm doing is wrong, please feel free to tell me.
Note 2: If any of you do or have done USACO, you might recognize this problem as the milk3 training gateway problem. This might aid you if you don't know what I'm doing here.
It sounds like you need to use pointer to member variable for the argument types in pour.
void pour(double threeBuckets::(*pourer) ,
double threeBuckets::(*receiver),
int receiverCap,
double threeBuckets::(*other)) {
...
}
In the function, change the use of
allCombinations[totalCombinations].pourer
allCombinations[totalCombinations].receiver
allCombinations[totalCombinations].other
by
allCombinations[totalCombinations].*pourer
allCombinations[totalCombinations].*receiver
allCombinations[totalCombinations].*other
respectively.
At the point of calling the function, use:
pour(&threeBuckets::bucketA,
&threeBuckets::bucketB,
0, // Any appropriate value
&threeBuckets::bucketC);
Another option that is worth considering is:
Change threeBuckets to use an array.
Change the arguments to pour to be indices to the array.
struct threeBuckets {
int buckets[3];
};
void pour(int pourerIndex ,
int receiverIndex,
int receiverCap,
int otherIndex)) {
...
}
Then, instead of using
allCombinations[totalCombinations].pourer
allCombinations[totalCombinations].receiver
allCombinations[totalCombinations].other
use
allCombinations[totalCombinations].buckets[pourerIndex]
allCombinations[totalCombinations].buckets[receiverIndex]
allCombinations[totalCombinations].buckets[otherIndex]
Of course, change the call to use indices.
pour(0,
1
0, // Any appropriate value
2);
I'm trying to use a static variable as a counter for the number of times a function has been called. Essentially, I'm having function A call function B a number of times, and I want function B to return that value to function A so it can be displayed. An example of my test code is below(here main is function A and showStat is function B). As of now the output is 012340; the desired output is 012344. Thanks in advance.
int showStat()
{
static int statNum;
cout<<statNum; //function check
statNum++;
return statNum;
}
int main()
{
int statNum;
for( int i = 0; i < 5 ; i++)
{
showStat();
}
cout<<statNum;
return 0;
}
In main, change
showStat();
to
statNum = showStat();
You have two variables called statNum. Apparently the counting takes place in the static variable inside showStat() function. But in main() without reading the return value of showStat(), you are just printing the uninitialized local variable, which the compiler happened to assign an initial value 0.
I hope someone can help me. In an effort to be more specific about what I really need, and trim down my code, I have changed from having a vector purely of my Class, to having a vector of objects of a new class, of which my original class is a type within.
I hope I have explained myself clearly up until this point. I will show the relevant classes:
class screen_area
{
private:
int my_id, my_x, my_y, my_width, my_height;
bool active=true;
public:
screen_area (int button_id=0, int x=0, int y=0, int width=0, int height=0, bool isactive=true)
{
my_id = button_id;
my_x = x;
my_y = y;
my_width = width;
my_height = height;
active = isactive;
}
~screen_area()
{}
class bet
{
private:
int wager = 0;
int multiplier = 0;
public:
screen_area area;
bet(int wager, int multiplier, screen_area area)
{};
~bet()
{};
There is a little more to them, but this is the bread and butter. Now previously I had used a member function within "screenarea", to return any value I had wanted from a specific object:
int getvalue(int value)
{
switch(value)
{
case 1 :
return my_id;
case 2 :
return my_x;
case 3 :
return my_y;
case 4 :
return my_width;
case 5 :
return my_height;
case 6 :
return active;
}
}
And I have modified a lookup function to use this member function on the screenarea that is a type contained within "bet".
int returnbuttonid(int mousex, int mousey, std::vector<bet> *buttons)
{
for (auto ep : *buttons )
{
if ((ep.area.getvalue(2) > mousex) && (ep.area.getvalue(3) > mousey))
{int id_value = ep.area.getvalue(1);
return id_value;
}
}
}
However... it returns garbage. I'm clearly missing something, but I am going through it logically and it all seems to make sense.
Sorry in advance if it is something simple! And I appreciate that this may seem long winded but I would really appreciate some help!
And just to be super clear... this is how I am calling it:
vector<bet> localbuttons; //Declaration of Vector
load_map("data.dat", &localbuttons); //load buttonmap using function
int buttonpressed = returnbuttonid(100,300, &localbuttons);
In response to a very speedy comment. It's clear that the problem at least starts with an unpublished piece of code. My vector of "bet" is not being filled with the arguments I am passing to it when I try to overload the constructor. I presumed I had corrected the syntax correctly when I created the new class "bet", but after probing the vector it is not showing any data.
In my function load_map:
bool load_map(std::string path, std::vector<bet> *buttons)
{
//setup file
ifstream inputFile( path.c_str() );
//
//The stuff in the middle here is irrelevant
//and I've take it out to make this tidier
buttons->push_back(bet(0,0, screen_area(id,x,y,width,height, true)));
}
return 0;
}
Now the only part of this that has changed since I had this function was working is:
buttons->push_back(bet(0,0, screen_area(id,x,y,width,height, true)));
So I am guessing this is where the problem originates. The variables are not overloading the default screen_area constructor. So when I:
cout << localbuttons[1].area.my_id << endl;
I always see whatever value I place in the default constructor. It is "0" in the constructor I have posted here, but if I change it, it changes correspondingly.
And I shouldn't have said garbage, I was at fault for thinking I had correctly identified the area of the problem, and trying to be concise. So I guess I should be asking first... How can I correctly overload this "screenarea" constructor?
The problem here was in the Constructor of the Bet class.
After having a look here:
http://www.cplusplus.com/doc/tutorial/classes/
I rewrote the constructor in the Bet class:
bet(int w, int m, int button_id=0, int x=0, int y=0,
int width=0, int height=0, bool isactive=true)
: area(button_id, x, y, width, height, isactive),
wager(w), multiplier(m)
{};
My apologies if I wasted anyone time with misdirection, and thanks for the sensible advice from Jonathon Potter.
I'm not sure why I thought you could call constructors within parentheses. My compiler didn't seem to complain about it, but from what I can gather - I was just creating a temporary object.
cliques is my class object. All my class commands work when I use them in my main but for some reason I cannot make changes to my heaps or stacks through my functions. I tried using reference markers on my function parameters but still I'm having ussues. Maybe I've done the reference incorrectly. Does anyone have any ideas what I might be doing wrong?
This is one of my functions:
void UpdateTopK(cliques C, vector<cliques> minheap) {
if (C.getclique_size() < CliqueSize) {
return;
}
else if (minheap.size() < Solutions) {
minheap.push_back(C);
push_heap(minheap.begin(), minheap.end(), min_iterator());
}
else if (minheap.size() == Solutions and C.getMaxclique_prob() > minheap.front().getMaxclique_prob()) {
pop_heap(minheap.begin(), minheap.end(), min_iterator());
minheap.pop_back();
minheap.push_back(C);
push_heap(minheap.begin(), minheap.end(), min_iterator());
}
This is part of my main:
stack <cliques> cstack;
vector<cliques> max_heap;
make_heap(max_heap.begin(), max_heap.end(), max_iterator());
vector<cliques> min_heap;
make_heap(min_heap.begin(), min_heap.end(), min_iterator());
for (int i = 0; i < 5; i++) {
cliques temp(i);
cstack.push(temp);
}
while (!cstack.empty()) {
cliques temp = cstack.top();
cstack.pop();
bool pruned = GenerateChildren(temp, min_heap, max_heap, cstack, graph);
if (!pruned) {
UpdateTopK(temp, min_heap);
}
}
You are passing arguments by value, this implies that parameters are copied before being passed to the function.
So every modification inside a method refers to the local copy only. Try passing values by references, eg:
void UpdateTopK(cliques& C, vector<cliques>& minheap)
^ ^
Mind that an object that needs to be passed to a function without copy and without being edited should be passed by const T& to specify this.
Here I have written some code to get the square of a number from a function, but the return statement is not working as desired by me, it is giving me the same number which I have entered, I want to know the reason behind this, please if any one can explain this to me...
#include<iostream>
#include<conio.h>
using namespace std;
int square(int &i);
int main()
{
cout<<"enter the number whose square you want to find";
int a;
cin>>a;
square(a);
cout<<"the square of the number is"<<a;
_getch();
return 0;
}
int square(int &i)
{
return i*i;
}
You're ignoring the returned value. You should store it as:
int value = square(a);
cout<<"the square of the number is "<< value;
Also, as the type is just integral type, passing by reference doesn't give you much advantage. I would suggest to use pass by value for its readability sake:
int square(int i)
{
return i*i;
}
--
Or in case if you're experimeting with reference, and trying to learn it, then in that case I would say that you've to store the result of product in the argument itself, as:
int square(int &i)
{
i = i * i; //this updates i here, and at the call site as well
return i;
}
Or simply do this:
int square(int &i)
{
return i = i*i; //multiply, update, and return - all in one statement!
}
You do not obtain the result.
Your line should be:
a = square(a);
to fetch the result from the function.
The other possibility would be to write in the function
int square(int &i)
{
i = i * i;
return i;
}
The latter will alter the variable you passed to the function which justifies passing a reference.
To make it clear you want to alter the variable do something like:
void square(int &i)
{
i = i * i;
}
You see there is no return involved but it will alter the variables value.
You have a choice:
Modify the parameter you pass in, or
Return a value and assign it to something in the calling scope.
What you are doing in square is the second option. You seem to want the first.
If what you really want is to modify the passed-in value, then what you need is this:
void square(int &i)
{
i = i*i;
}
Either do it this way:
a = Square (a) ; // in main()
...
int Square (int i) // Pass by value -- doesn't change a in main
{
return i * i ;
}
or do it this way:
Square (a) ; // in main()
...
void Square (int& i) // Pass by reference -- changes a in main
{
i = i * i ; // No need for a return value
}
Make sure you understand the difference before you program anything else!
Judging by your comments on the answers, you've misunderstood what passing by reference does OR you've misunderstood return.
I'm assuming you're thinking that the variable i will be updated in your program. However, this is not the case. If you did something like...
i = i*i;
then yes, you would be correct. However, you did not assign any value to i, you simply multiplied it by itself and returned the result. Also, if you truly wanted to make this work based on a reference, there would be no need to return anything, as the variable would be updated via the reference.