How do I make it so I can plug in the random value of a and b into the system.out.println so it will display in the console window what the random number was?
public class MoreIfStmts {
/* Chase Pittman
* This program compares two variables and tells which one is greater or if they're equal.
*/
public static void main(String[] args) {
int q=0;
while (q < 10) {
q=q+1;
int a=0;
int b=0;
a=(int) (Math.random() * 10);
b=(int) (Math.random() * 10);
if (a > b)
{
System.out.println ("Blue is better than red.");
} // This is the end of the then clause.
else
{
if (a < b)
{
System.out.println ("Red is better than blue.");
} // This is the end of the if clause.
else
if (a == b)
{
System.out.println ("Blue is as good as red.");
} // This is the end of the second else clause.
} // This is the end of the first else clause.
} // This is the end of while statement.
} // This is the end of main.
} // This is the end of class MoreIfStmts.
System.out.println ("Red is better than blue."+ " a="+a+ " b="+b);
You may also use formatted output:
System.out.printf("Blue is better than red. a = %d, b = %d\n", a, b);
Related
I am trying to understand how I could implement a concurrent thread for processing data in a Winrt/Cpp application.
As background
I have implemented a winRT BLE component that wraps the windows bluetooth function
I am using this component in my winrt application and successfully get a notification when the app connects to me bluetooth device
Now within the app I would like to "spawn" a process that continually sends a request to the BLE device and process the response.
To achieve #3 I thought one approach could be - within the connection notification I would invoke a function called StartDataAcq that uses the threadpool to schedule work,
to test out this approach I decided to just use the example shown here
https://learn.microsoft.com/en-us/windows/uwp/threading-async/submit-a-work-item-to-the-thread-pool
to see if it could work
So the implementation looks like this within my code
void Datamanager::BleFound(
winrt::Windows::Foundation::IInspectable const& /* sender */,
uint32_t foundFlags)
{
OutputDebugStringW((L"Member function Called from DataManager->" + hstring(std::to_wstring(foundFlags)) + L"\r\n").c_str());
if (!acqStarted)
{
StartDataAcq();
acqStarted = true;
}
}
void DataManager::StartDataAcq()
{
// The nth prime number to find.
const unsigned int n{ 99999999 };
unsigned long nthPrime{ 0 };
//submit work to thread poool
m_workItem = Windows::System::Threading::ThreadPool::RunAsync([&](Windows::Foundation::IAsyncAction const& workItem)
{
unsigned int progress = 0; // For progress reporting.
unsigned int primes = 0; // Number of primes found so far.
unsigned long int i = 2; // Number iterator.
if ((n >= 0) && (n <= 2))
{
nthPrime = n;
return;
}
while (primes < (n - 1))
{
if (workItem.Status() == Windows::Foundation::AsyncStatus::Canceled)
{
break;
}
// Go to the next number.
i++;
// Check for prime.
bool prime = true;
for (unsigned int j = 2; j < i; ++j)
{
if ((i % j) == 0)
{
prime = false;
break;
}
};
if (prime)
{
// Found another prime number.
primes++;
// Report progress at every 10 percent.
unsigned int temp = progress;
progress = static_cast<unsigned int>(10.f * primes / n);
if (progress != temp)
{
std::wstringstream updateString;
updateString << L"Progress to " << n << L"th prime: " << (10 * progress) << std::endl;
OutputDebugStringW((L"" + updateString.str() + L"\r\n").c_str());
// Update the UI thread with the CoreDispatcher.
/*
Windows::ApplicationModel::Core::CoreApplication::MainView().CoreWindow().Dispatcher().RunAsync(
Windows::UI::Core::CoreDispatcherPriority::High,
Windows::UI::Core::DispatchedHandler([&]()
{
UpdateUI(updateString.str());
}));
*/
}
}
}
// Return the nth prime number.
nthPrime = i;
} , Windows::System::Threading::WorkItemPriority::Normal, Windows::System::Threading::WorkItemOptions::TimeSliced);
}
I see the message for the connect notification,
This debug string - OutputDebugStringW((L"Member function Called from DataManager->" + hstring(std::to_wstring(foundFlags)) + L"\r\n").c_str());
however I never see any output from the async workitem.
Can someone please help me spot the issue?
Also are there any better ways to do this? I was reading about co-routines but seeing how the work is data processing locally I do not think a co routine would work
I also was trying to find out how I could spawn a separate thread and manage it within my code - but am not sure how to do it within the winrt/c++ framework
based on Raymond Chen's comment I converted the variables on the stack to std::shared_ptr and the sample works now...
Also stumbled upon this link that explains this better than I can...
https://learn.microsoft.com/en-us/cpp/parallel/concrt/task-parallelism-concurrency-runtime?view=msvc-170#lambdas
void DataManager::StartDataAcq()
{
auto n = make_shared<UINT32>(9999);
auto nthPrime = make_shared<UINT32>(0);
m_workItem = Windows::System::Threading::ThreadPool::RunAsync([n,nthPrime](Windows::Foundation::IAsyncAction const& workItem)
{
unsigned int progress = 0; // For progress reporting.
unsigned int primes = 0; // Number of primes found so far.
int i = 2; // Number iterator.
if ((*n >= 0) && (*n <= 2))
{
*nthPrime = *n;
//return;
}
while (primes < (*n - 1))
{
if (workItem.Status() == Windows::Foundation::AsyncStatus::Canceled)
{
break;
}
// Go to the next number.
i++;
// Check for prime.
bool prime = true;
for (unsigned int j = 2; j < i; ++j)
{
if ((i % j) == 0)
{
prime = false;
break;
}
};
if (prime)
{
// Found another prime number.
primes++;
// Report progress at every 10 percent.
unsigned int temp = progress;
progress = static_cast<unsigned int>(10.f * primes / *n);
if (progress != temp)
{
std::wstringstream updateString;
updateString << L"Progress to " << *n << L" " << i << L" th prime: " << (10 * progress) << std::endl;
OutputDebugStringW((L"" + updateString.str() + L"\r\n").c_str());
// Update the UI thread with the CoreDispatcher.
/*
Windows::ApplicationModel::Core::CoreApplication::MainView().CoreWindow().Dispatcher().RunAsync(
Windows::UI::Core::CoreDispatcherPriority::High,
Windows::UI::Core::DispatchedHandler([&]()
{
UpdateUI(updateString.str());
}));
*/
}
}
}
// Return the nth prime number.
*nthPrime = i;
std::wstringstream updateString;
updateString << L"Found the nth prime " << i << std::endl;
OutputDebugStringW((L"" + updateString.str() ).c_str());
} , Windows::System::Threading::WorkItemPriority::Normal, Windows::System::Threading::WorkItemOptions::TimeSliced);
}
So, I know that there are many people with this problem and many questions about it, but I just couldn't fin a solution for this, every other thing I try to execute works, but this doesn't and I can't figure out why...
package prob3;
public class LargestPrimeFactor {
double num = 600851475143D;
double LargestPrimeFactor;
public void getLargestPrimeFactor(String [] args){
double prevPrimeFactor = 0;
do {
for(double i = 0; i < num/2; i++){
if((num % i == 0) && (num / i != 1)){
prevPrimeFactor = num;
LargestPrimeFactor = num / i;
} else {
continue;
}
}
} while(prevPrimeFactor != LargestPrimeFactor);
System.out.println("The biggest prime factor of " + num + " is " + LargestPrimeFactor);
}
}
you should define a main function to run your program. Something like:
public static void main(String[] args) {
getLargestPrimeFactor(args);
}
I'm trying to build a 2D sparse matrix class using std::map, which should be called in (for example) the following way:
SparseMatrix<double> M(2,2); // Create a new sparse matrix with 2 rows and 2 columns
M[{1,1}] = 3.1; // Sets element {1,1} to 3.1
The following class can perform these tasks:
template < typename T >
class SparseMatrix
{
std::map< array<int, 2>, T> data;
const array<int, 2> size;
public:
SparseMatrix(const int rows, const int cols)
: size({ rows, cols }) {}
// []-operator to set and get values from matrix
T& operator[](const array< int,2 > indices)
{
// Check if given indices are within the size of the matrix
if(indices[0] >= size[0] || indices[1] >= size[1])
throw invalid_argument("Indices out of bounds");
return data[indices];
}
};
Using this class it is possible to create a new object and set the element, however, the []-operator is also used to get elements, for example:
std::cout << M[{1,1}] << std::endl;
The problem with this is that if this is used to get an element that is not set already, it creates a new part in the map with the given indices and a value of 0, which is undesired for a sparse matrix class, as the map should only contain the non-zero elements.
Is it possible to solve this problem with the []-operator by making a distinction between 'setting' and 'getting'? In case of 'getting' should the operator only return a 0 without adding it to the map.
You can differentiate between reading and writing by using a proxy instead of a T&. Only showing the relevant code:
template <typename T>
class SparseMatrixProxy {
public:
//for reading an element:
operator T() const {
// Check if given indices are within the size of the matrix
if (indices[0] >= matrix.size[0] || indices[1] >= matrix.size[1])
throw std::invalid_argument("Indices out of bounds");
auto map_it = matrix.data.find(indices);
if (map_it == matrix.data.end()) {
return T{};
}
return map_it->second;
}
//for writing an element:
auto operator=(const T &t) {
//optional: when setting a value to 0 erase it from the map
if (t == T{}) {
matrix.data.erase(indices);
} else {
matrix.data[indices] = t;
}
return *this;
}
};
to be used in SparseMatrix like this:
// []-operator to set and get values from matrix
SparseMatrixProxy<T> operator[](const std::array<int, 2> indices) {
return {*this, indices};
}
With usage:
SparseMatrix<double> M(2, 2); // Create a new sparse matrix with 2 rows and 2 columns
M[{{1, 1}}] = 3.1; // Sets element {1,1} to 3.1
std::cout << M[{{1, 1}}] << '\n';
assert(M.mapsize() == 1); //1 element for index {1,1}
std::cout << M[{{0, 0}}] << '\n';
assert(M.mapsize() == 1); //still 1 element because reading doesn't insert an element
M[{{1, 1}}] = 0;
assert(M.mapsize() == 0); //0 elements because we set the only non-0 element to 0
Complete example.
There is std::map::find method. It returns an iterator and if it equals to map.end() then it means that the element is absent in the map.
Yup, it's a pain in the backside. Luckily the clever C++11 bods realised this and gave us a new method: at.
Use the at method (available from the C++11 standard onwards), which does not do any insertion, although you still need a catch handler for a possible std::out_of_range exception.
See http://en.cppreference.com/w/cpp/container/map/at
It's cheaper from performance point of view to implement sparse matrix by creating own mapping, e.g via storing indices.
template<typename T>
class SparseMatrix
{
...
int m, n;
vector<T> values;
vector<int> cols;
vector<int> rows;
}
template<typename T>
T SparseMatrix<T>::get(int row, int col) const
{
this->validateCoordinates(row, col);
int currCol = 0;
for (int pos = rows.at(row - 1) - 1; pos < rows.at(row) - 1; pos++)
{
currCol = cols.at(pos);
if (currCol == col)
return vals.at(pos);
else if (currCol > col)
break;
}
return T();
}
template<typename T>
SparseMatrix<T> & SparseMatrix<T>::set(T val, int row, int col)
{
// Validate coordinates here?
int pos = rows.at(row - 1) - 1;
int currCol = 0;
for (; pos < rows.at(row) - 1; pos++) {
currCol = cols.at(pos);
if (currCol >= col) {
break;
}
}
if (currCol != col) {
if (!(val == T())) {
this->insert(pos, row, col, val);
}
} else if (val == T()) {
this->remove(pos, row);
} else {
vals.at(pos) = val;
}
return *this;
}
template<typename T>
void SparseMatrix<T>::insert(int index, int row, int col, T val)
{
vals.insert(vals.begin() + index, val);
cols.insert(cols.begin() + index, col);
for (int i = row; i <= this->m; i++)
rows.at(i) = rows.at(i) + 1;
}
And so on...
I'm trying to translate a, b, c, d = iterable to Python's C/API.
I'm looking for a function similar to PyArg_ParseTuple, just for iterables.
In other words, something in the area of PyIter_Parse or PyObject_ParseIterable, if such functions would have existed.
Any tips how to implement it?
No, there is no helper function that can do this for you.
You'd have to use PyIter_Next() up to max times to retrieve values, raise an exception when you can't get at least min values, and then just build a tuple from that.
Something like (untested, largely pilfered from PySequence_Tuple()):
int
PyIter_LimitedTuple(PyObject *v, Py_ssize_t min, Py_ssize_t max)
{
PyObject *it; /* iter(v) */
PyObject *result = NULL;
Py_ssize_t j;
it = PyObject_GetIter(v);
if (it == NULL)
return NULL;
/* allocate space. */
result = PyTuple_New(max);
if (result == NULL)
goto Fail;
/* Fill the tuple. */
for (j = 0; ; ++j) {
PyObject *item = PyIter_Next(it);
if (item == NULL) {
if (PyErr_Occurred())
goto Fail;
break;
}
if (j > max) {
PyErr_Format(PyExc_ValueError,
"too many values to unpack");
goto Fail;
}
PyTuple_SET_ITEM(result, j, item);
}
if (j < min) {
PyErr_Format(PyExc_ValueError,
"need more than %d value to unpack",
j);
goto Fail;
}
/* Cut tuple back if fewer than max items were available. */
if (j < max &&
_PyTuple_Resize(&result, j) != 0)
goto Fail;
Py_DECREF(it);
return result;
Fail:
Py_XDECREF(result);
Py_DECREF(it);
return NULL;
}
then pass the resulting tuple to PyArg_UnpackTuple().
I'm learning java and I'm having an issue with my if code not running.
In the following code I'm trying to determine if a number (variable num) is a triangle number (1,3, 6, 10 etc). The code should run through and give the "Is Triangle". However it keeps spitting out Null.
I understand this is not the most effective way to do this code, but I am trying to learn how to use Classes.
public class HelloWorld {
public static void main(String[] args) {
class NumberShape {
int num = 45;
int tri = 0;
int triplus = 0;
String triresult;
public String triangle() {
while (tri < num) {
if (tri == num) {
triresult = "Is a Triangle";
System.out.println("Is a Triangle");
} else if (tri + (triplus + 1) > num){
triresult = "Is Not a Triangle";
} else {
triplus++;
tri = tri + triplus;
}
}
return triresult;
}
}
NumberShape result = new NumberShape();
System.out.println(result.triangle());
}
}
Thanks for any help provided.
Try this code :
public class HelloWorld {
public static void main(String[] args) {
class NumberShape {
int num = 10;//Try other numbers
int tri = 0;
int triplus = 0;
int res = 0;
String triresult = "Is Not a Triangle";
int[] tab= new int[num];
public String triangle() {
//to calculate the triangle numbers
for(int i = 0; i<num; i++){
res = res + i;
tab[i]=res;
}
//To check if num is a triangle or not
for(int i = 0; i<tab.length; i++){
System.out.println(">> " + i + " : " + tab[i]);
if(tab[i]== num){
triresult = num + " Is a Triangle";
break;//Quit if the condition is checked
}else{
triresult = num + " Is Not a Triangle";
}
}
return triresult;
}
}
NumberShape result = new NumberShape();
System.out.println(result.triangle());
}
}
Hope this Helps.
Step through the loop carefully. You'll probably see that there is a case where
(tri < num)
fails, and thus you fall out of the loop, while
(tri == num)
and
(tri + (triplus + 1) > num)
both fail too, so no text gets set before you fall out.
You probably want to do your if-tests within the method on just tri, not a modification of tri, so as to reduce your own confusion about how the code is working.