c++,polar-coordinates,cartesian-coordinates , Incorrect Polar - Cartesian Coordinate Conversions. What does -0 Mean?

## Question:

Tag: c++,polar-coordinates,cartesian-coordinates

I am getting incorrect conversions from polar to cartesian coordinates and vice versa. My code produces weird points like (1,-0). Im using this calculator to check my conversions. Also one of the conversions is completely wrong when I convert back to cartesian coordinates.

Point b: (0,1) => (1,1.5708) => (0,0)

``````#include <math.h>
#include <iostream>
/* Title:      Polar - Cartesian Coordinate Conversion
*  References: HackerRank > All Domains > Mathematics > Geometry > Polar Angles
*              Cartesian to Polar: (radius = sqrt(x^2 + y^2), theta = atan(y/x))
*/

//General 2D coordinate pair
struct point{
point(float a_val, float b_val) : a(a_val), b(b_val){;};
point(void){;};
float a, b;
};
//Converts 2D Cartesian coordinates to 2D Polar coordinates
point to_polar(/*const*/ point& p){//*** Conversion of origin result in (r, -nan) ***
point ans(sqrt(pow(p.a,2) + pow(p.b,2)), atan(p.b/p.a));
return ans;
}
//Converts 2D Polar coordinates to 2D Cartesian coordinates
point to_cartesian(/*const*/ point& p){
point ans(p.a * cos(p.b), p.a * sin(p.b));
return ans;
}
//Outputs 2D coordinate pair
std::ostream& operator<<(std::ostream& stream, const point& p){
stream << "(" << p.a << "," << p.b << ")";
return stream;
}
int main(){
//Test Points - Cartesian
point a(0, 0);
point b(0, 1);
point c(1, 0);
point d(0,-1);
point e(-1,0);

//Print Cartesian/Rectangular points
std::cout << "Cartesian Coordinates:" << std::endl;
std::cout << a << std::endl;
std::cout << b << std::endl;
std::cout << c << std::endl;
std::cout << d << std::endl;
std::cout << e << std::endl;

//Print Cartesian to Polar
std::cout << "Polar Coordinates:" << std::endl;
std::cout << to_polar(a) << std::endl;//Failure (0,-nan)
std::cout << to_polar(b) << std::endl;//Success
std::cout << to_polar(c) << std::endl;//Success
std::cout << to_polar(d) << std::endl;//Success
std::cout << to_polar(e) << std::endl;//Failure (1,-0)

//Print Polar to Cartesian
std::cout << "Cartesian Coordinates:" << std::endl;
std::cout << to_cartesian(a) << std::endl;//Success
std::cout << to_cartesian(b) << std::endl;//Failure (0,0)
std::cout << to_cartesian(c) << std::endl;//Success
std::cout << to_cartesian(d) << std::endl;//Failure (0,-0)
std::cout << to_cartesian(e) << std::endl;//Failure (-1,-0)

return 0;
}
``````

You are converting to cartesian the points which are in cartesian already. What you want is:

``````std::cout << "Cartesian Coordinates:" << std::endl;
std::cout << to_cartesian(to_polar(a)) << std::endl;
std::cout << to_cartesian(to_polar(b)) << std::endl;
//...
``````

Edit: using `atan2` solves the NaN problem, `(0, 0)` is converted to `(0, 0)` which is fine.

# Related:

## No match for 'operator*' error

c++,c++11
Hello fellow programmers! I was going to write a small program for calculating total pay for different periods of time depending on the amount of hours and the salary that the user enters. I managed to make a small bit of the program but when I try to run it...

## Explicit instantiation of class template not instantiating constructor

c++,templates,constructor,explicit-instantiation
I'm working on a project in C++ and am having trouble understanding what members of a template class get explicitly instantiated when I explicitly instantiate the template class. I've written the following file, which I then compile using Visual C++ 2008 Express Edition's Release configuration and then pop into a...

## Why are shaders and programs stored as integers in OpenGL?

I'm following the "OpenGL Superbible" book and I can't help but notice that when we create a shader and create the program that we attach the shaders to, we store them as GLuint which are unsigned integers. Why are they stored as numbers? What does the value of the number...

## template template class specialization

c++,templates,template-specialization
I am just learning about Template Template class specialisation. Not a big problem to explain in detail. From my understanding std::uniform_int_distribution is a template whereas std::uniform_int_distribution<Type> is the full specialisation of uniform_int_distribution giving a type. I pass this in the specialisation class template as follows below Main class template <template...

## C++11 Allocation Requirement on Strings

c++,string,c++11,memory,standards
I had heard that C++11 was going to require strings to be allocated in contiguous memory. I even thought I saw a stack overflow question on it, but I can't seem to find it. I know that in practice both gcc and Visual Studio do allocate strings contiguously, I'm just...

## How can I access the members of a subclass from a superclass with a different constructor?

c++,inheritance,constructor,subclass,superclass
I have the following class and typedef: class Object { protected: long int id; public: Object(void); ~Object(void) {}; long int get_id(void); }; typedef map<string, Object> obj_map; And then I have its child: class Image: public Object { private: path full_path; int x; int y; img image; public: Image(path p, int...

## Add more features to stack container

c++,visual-c++,stl
I am using default features(push, pop, top, empty, size) of stack container of STL. If I want to add more features like access an element from middle of stack. How could I do this? Thanks...

## How can I convert an int to a string in C++11 without using to_string or stoi?

c++,string,c++11,gcc
I know it sounds stupid, but I'm using MinGW32 on Windows7, and "to_string was not declared in this scope." It's an actual GCC Bug, and I've followed these instructions and they did not work. So, how can I convert an int to a string in C++11 without using to_string or...

## MFC visual c++ LNK2019 link error

c++,mfc
I just don't understand why i can use the public variables on the class but are getting a link error when trying to use the getLicenceRefused method. I wasn't sure if the problem was because of the CString copy constructor problem I have had before so took the parameter out,...

## Algorithm for [inclusive/exclusive]_scan in parallel proposal N3554

c++,algorithm,parallel-processing,c++14
Proposal N3554 (A Parallel Algorithms Library) for C++14, proposes (among other things), what seem to be parallel versions of the current std::partial_sum, e.g.: template< class ExecutionPolicy, class InputIterator, class OutputIterator, class BinaryOperation> OutputIterator inclusive_scan( ExecutionPolicy &&exec, InputIterator first, InputIterator last, OutputIterator result, BinaryOperation binary_op); With the explanation Effects: For each...

## Test if string represents “yyyy-mm-dd”

c++,command-line-arguments
I am working on a program that takes two command line arguments. Both arguments should be dates of the form yyyy-mm-dd. Since other folks will be using this program and it will be requesting from mysql, I want to make sure that the command line arguments are valid. My original...

## C++ template template

c++,templates
I'm trying to understand C++ template templates by implementing a generic container class. Here is the code: using namespace std; template <typename T, template <typename STORETYPE> class Container> class Store { public: ~Store() {}; Store() {}; void someFunc( const T & ) {}; //... private: Container<T> storage; }; int main(int...

## create vector of objects on the stack ? (c++)

c++,vector,heap-memory
I am creating a temporary vector of pointers to myObject objects. But I am wondering about what happens to the objects I created... { std::vector<myObject *> myVector; myVector.reserve(5); for (int i = 0 ; i < 5 ; ++i){ myVector[i] = new myObject(); } } I assume that at the...

## C++ Isn't this a useless inline declaration?

c++,inline,private,member,protected
This is another question about inlining a function. But I will take possible comments and answers right away: Defining a function inside a class makes it inline automatically. The same behaviour can be achieved by marking a function with inline outside of the class. An inline function doesn't have to...

## Copy text and placeholders, variables to the clipboard

c++,qt,clipboard
In my application I want generate random numbers or strings with a text in front of it. It is important for me that the text won't appear in my window, but instead gets copied to the clipboard. int randomnumber = rand() % 46 + 1; QClipboard *cb = QApplication::clipboard(); cb->setText("Just...

## Undefined behaviour or may be something with memset

c++,undefined-behavior
I was trying to save the binary equivalent of a 32 bit number in an array A. For testing my showbits() function , I choosed 8,9 when I came across this thing: I am facing an unreasonable thing in my code when I am placing memset in the function showbits(),I...

## Storing columns on disk and reading rows

c++,file,matrix,io
So I have a C++ code that finds the inverse of a square matrix. The inverse is full and it would be bad to keep it all in memory because I am working with hundreds of thousands of columns. My code generates the columns one by one. After finding the...

## pointer to pointer dynamic array in C++

c++,arrays,pointers
I've been having bad luck with dynamic pointers when I want to close it. why the application wrote to memory after end of heap buffer? how can I close my array? int main() { . . int **W; W = new int* [n]; for (int i=1; i <= n; i++)...

## .cpp:23: error: cannot convert ‘std::string’ to ‘const char*’ for argument ‘1’ to ‘int atoi(const char*)’

c++,string
Here a basic code I'm trying to run But I'm having trouble with stoi (it's c++) I keep getting error: ‘stoi’ was not declared in this scope I tried atoi and strtol with this error .cpp:23: error: cannot convert ‘std::string’ to ‘const char*’ for argument ‘1’ to ‘int atoi(const char*)’...

## Validate case pattern (isupper/islower) on user input string

c++,user-input
I need to write a program that checks if the user-provided first and last names are correctly typed. The program needs to validate that only the first letter of each name part is uppercase. I managed to write code that checks the first character of the input. So I have...

## Can python script know the return value of C++ main function in the Android enviroment

python,c++
There are several ways of calling C++ executable programs. For example, we can use def run_exe_return_code(run_cmd): process=subprocess.Popen(run_cmd,stdout=subprocess.PIPE,shell=True) (output,err)=process.communicate() exit_code = process.wait() print output print err print exit_code return exit_code to process a C++ executable program: run_exe_return_code('abc') while abc is created by the following C++ codes: int main() { return 1;...

## Implicit use of initializer_list

c++,c++11,initializer-list
§[dcl.init.list] 8.5.4/2: The template std::initializer_list is not predefined; if the header <initializer_list> is not included prior to a use of std::initializer_list — even an implicit use in which the type is not named (7.1.6.4) — the program is ill-formed. Does that mean this program is ill-formed? #include <vector> int main()...

## Make a triangle shape in C++

c++
I am trying to print out the shape of a triangle but I am kinda lost... this is what I have so far: #include <iostream> using namespace std; int main() { int i, k, n; cout << "Please enter number of rows you want to see: \n"; cin >> n;...

## undefined reference to `vtable for implementation' error

c++,build,makefile
I wrote some c++ files and after compiling with out make file it works fine . But when using make file it pop out some errors . My codes are : include directory files : application.h #ifndef APPLICATION_H #define APPLICATION_H #include "employee.h" #include "employee_data.h" #include "employee.h" ...some defintions here... #endif...

## opencv window not refreshing at mouse callback

c++,opencv
I am trying to draw with mouse move in an opencv window. But when I draw, nothing draws on the window. When I try to close the window from the cross in the topleft(ubuntu), it opens a new window which it should be as I haven't pressed escape, and in...

## Passing something as this argument discards qualifiers

c++,c++11
Using the below code, i get the following compile error: In static member function ‘static std::string ctedata::Record::getDispatcher<std::basic_string<char> >::impl(const ctedata::Record&, const string&)’: /home/jason/CrownTheEmpire/lib/ctedata/data.h:111:38: error: passing ‘const std::map<std::basic_string<char>, std::basic_string<char> >’ as ‘this’ argument discards qualifiers [-fpermissive] return rec.fieldValues_[field]; ^ In file included from /usr/include/c++/5.1.0/map:61:0, from...

## std::condition_variable – notify once but wait thread wakened twice

Here's a simple C++ thread pool implementation. It's an altered version orginated from https://github.com/progschj/ThreadPool. #ifndef __THREAD_POOL_H__ #define __THREAD_POOL_H__ #include <vector> #include <queue> #include <memory> #include <thread> #include <chrono> #include <mutex> #include <condition_variable> #include <future> #include <functional> #include <stdexcept> namespace ThreadPool { class FixedThreadPool { public: FixedThreadPool(size_t); template<class F, class......

## Method returning std::vector>

c++
As a continuation of a: Thread, I came across a problem with writing a method of a class which returns: std::vector<std::unique_ptr<Object>> I get compiler errors when such a return type is written. There is some problem with delete operand or something ... Generally, I've wanted to write a method which...

## Same function with and without template

c++,c++11
I am trying to understand a piece of code of C++11. A class contains 2 functions as shown below: class abc { public: void integerA(int x); template<typename typ> void integerA(typ x); }; I am unable to understand benefit of declaring 2 same functions. Why not declare only one template function?...

python,c++,ctypes
I have a simple test function on C++: #include <stdio.h> #include <string.h> #include <stdlib.h> #include <locale.h> #include <wchar.h> char fun() { printf( "%i", 12 ); return 'y'; } compiling: gcc -o test.so -shared -fPIC test.cpp and using it in python with ctypes: from ctypes import cdll from ctypes import c_char_p...

## How can I tell clang-format to follow this convention?

c++,clang-format
I would like to have this: if (!enabled) { return; } turned to this: if (!enabled) { return; } (In other words, I want short if-statements on a single line but keep the {} around them) Currently I'm using the following configuration: AllowShortIfStatementsOnASingleLine: true AllowShortLoopsOnASingleLine: true AllowShortCaseLabelsOnASingleLine: true AllowShortFunctionsOnASingleLine: true...

## Checking value of deleted object

c++
I asked a question: Detecting if an object is still active or it has been destroyed Considering that I cannot use libraries, there are no good out of the box solutions in C++. So, is it a bad practice to check if the object has been destroyed by analyzing memory...

## C++ & Qt: Random string from an array area

c++,arrays,string,qt,random
In my small Qt application, I want to pick a random string out of an array after I clicked on a button. I've read many threads but nothing works for me. So in my slot there's an array with several strings in it. I also implemented <string>, <time.h> and srand....

## OpenCV - Detection of moving object C++

c++,opencv
I am working on Traffic Surveillance System an OpenCv project, I need to detect moving cars and people. I am using background subtraction method to detect moving objects and thus drawing counters. I have a problem : When two car are moving on road closely them my system detects it...

## Passing iterator's element to a function: wrong type of pointer

c++,pointers,stl,iterator
I'm attempting to solve Project Euler's problem #3 using C++ to gain an understanding of how to use C++ iterators. According to the examples I've seen online, I can use the dereferened iterator as a parameter for cout, and it will print the elements successfully. By that same logic, I...

## Marshal struct in struct from c# to c++

c#,c++,marshalling
I have the following structures in C# and C++. C++: struct TestA { char* iu; }; struct TestB { int cycle1; int cycle2; }; struct MainStruct { TestA test; TestB test2; }; C#: [StructLayout(LayoutKind.Sequential, CharSet=CharSet.Ansi, Pack = 1)] internal struct TestA { [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 36)] private string iu; public...

## Type function that returns a tuple of chosen types

c++,templates,c++11,metaprogramming
I've implemented a type function Tuple that turn a list of My_enum values into an std::tuple of corresponding types: #include <tuple> enum My_enum{ t_int, t_double }; // Bind_type is a type function that given a My_enum returns the corresponding type template<My_enum E> struct Bind_type; template<> struct Bind_type<t_int>{ using type =...

## Strings vs binary for storing variables inside the file format

c++,file,hdf5,dataformat
We aim at using HDF5 for our data format. HDF5 has been selected because it is a hierarchical filesystem-like cross-platform data format and it supports large amounts of data. The file will contain arrays and some parameters. The question is about how to store the parameters (which are not made...

## segfault accessing qlist element through an iterator

c++,iterator,qlist
I get a segfault while iterating over a QList. I don't understand what I am doing wrong. I have a QList of Conversation. Inside a Conversation I have a QList of Msg. Below are the class description : Msg class : class Msg { public: Msg(); Msg(const Msg& other); Msg&...

## how to sort this vector including pairs

c++,vector
I want to sort in ascending order according to the first element of the inner pair, i.e. a in this case. But its not at all sorting. I am not sure if my function func logic is correct. #include<iostream> #include<algorithm> #include<vector> using namespace std; bool func(const pair<int,pair<int,int> >&i , const...

## Translating a character array into a integer string in C++

c++,arrays,string
I was trying to achieve translating a character array into a integer string and corresponding character to their alphabetical order. For instance: A(a) = 0 , Z(z) = 25. string key_char = argv[1]; string key_num; for (int i = 0; i < key_char.length(); i++){ if (isalpha(key_char[i])){ if (islower(key_char[i])){ key_num[i] =...

## Parameters to use in a referenced function c++

c++,pointers,reference
I am very confused as to what kind of variables I would put into my function here: names. I am doing a practice problem in a C++ book, because I am learning C++ and am on References and pointers right now, and cannot find a solution. Just for background information,...

## Incorrect Polar - Cartesian Coordinate Conversions. What does -0 Mean?

c++,polar-coordinates,cartesian-coordinates
I am getting incorrect conversions from polar to cartesian coordinates and vice versa. My code produces weird points like (1,-0). Im using this calculator to check my conversions. Also one of the conversions is completely wrong when I convert back to cartesian coordinates. Point b: (0,1) => (1,1.5708) => (0,0)...

## c++ extend constructor of same class (no inheritance)

c++,constructor
I might have found my answer somewhere here, but nevertheless, I'd like to be sure. I am making something represented in a graph (hence the nodes), and I wondered if this code of the constructors is working the way I think. G++ doesn't complain. I have the following class: #ifndef...

## Confused about returns in stack template

c++,templates,generic-programming
I'm implementing a generic stack (with an array) in C++ and am confused about what to return in this situation: template <class T> T Stack<T>::pop(void) { if (size != 0) { return items[size - 1]; size--; } else { cerr << "Cannot pop from empty stack." << endl; return ???;...

## dispatch response packet according to packet sequence id

c++,boost,boost-asio
I have a third-part server, and I'm writing a dll interface for it, my clients use my dll to communicate with the server. The protocol uses a long tcp connection, all traffic goes from this tcp connection. There could be sending/receiving multiple packets at the same time, like a send_msg...

## 3 X 3 magic square recursively

c++,algorithm,math,recursion
I'm trying to find all possible solutions to the 3X3 magic square. There should be exactly 8 solutions. My code gets them all but there are a lot of repeats. I'm having a hard time tracking the recursive steps to see why I'm getting all the repeats. // This program...

## Issue when use two type-cast operators in template class

c++
I define a template class in which, I define two type-cast operator template <class base_t> struct subclass { base_t base; //any function which defined for 'base_t' can be used with 'subclass<base_t>' operator base_t&() { return base; } //I want 'subclass<base_t>' can be converted to any class which 'base_t' can //I...

## Get an ordered list of files in a folder

c++,boost,boost-filesystem
I have used boost::filesystem::directory_iterator in order to get a list of all the available files into a given folder. The problem is that I supposed this method would give me the files in alphabetical order, while the results seem pretty random. Is there any fancy way of alphabetically sorting them?...