I saw, that there are libraries, that offer data types like BigInterger, but I need one, that contains a variable type, that is "big" (means: that can handle very high values) but also I need the possibility to divide it by another high number, so it wouldn't work with BigInterger..
If you need more precision in your calculations, you can use this library for big nums. Its simple and easy to start and created in C++ with template classes.
#include <ttmath/ttmath.h>
#include <iostream>
int main()
{
// Big<exponent, mantissa>
ttmath::Big<1,2> a,b,c;
a = "1234.3323454";
b = "3456.1234534";
c = a*b;
std::cout << c << std::endl;
}
Related
For the following code:
#include <iostream>
using namespace std;
class Hall
{
public:
double cost;
};
int main()
{
Hall hall;
hall.cost=10000.50;
cout<<hall.cost;
return 0;
}
Why does this code output 10000.5 and not 10000.50, can someone explain the logic behind this?
can someone explain the logic behind this?
The default behaviour is not show any trailing zeroes.
double (and floating-point variables in general) don't store a specific spelling of the number (base-10 or otherwise). That would be way too inefficient, and the ability to store meaningless zeroes would waste memory.
Instead, the numbers are encoded in a certain binary format. Printing them reproduces the base-10 spelling from binary.
By default, C++ does not display trailing zeros, however the standard library <iomanip> can be used along with std::fixed from <iostream>. Here is an example:
#include <iostream>
#include <iomanip>
int main() {
double myVar = 123.4;
std::cout << std::fixed << std::setprecision(2); // 2 trailing digits
std::cout << myVar << std::endl;
return 0;
}
I've been given the task to refactor a bunch of C++ code that has a lot of math and not an explanation of what it does.
In order to do that I've setup a bunch of automated test that given random data compare old and new code results.
The thing is that, while it is simple to generate random vector of any size I have a lot of "struct" with many public fields (> 20) I'm a bit tired of writing custom function to fill them.
One can think of using some kind of script to parse the definition and autobuild the corresponding generator function.
Do you think this is a good idea ?
Is there anything like that already done?
If you have only Plain Old Data, a struct is, roughly, merely a blob of memory with some meaning to the compiler.
This means you can treat it as such, and simply fill it with random bytes, using a union:
struct a {
int i;
char c;
float f;
double d;
};
union u {
char arr[sizeof(a)];
a record;
};
char generateRandomChar(); // implement some random char generation
int main() {
u foo;
for (char& c : foo.arr) {
c = generateRandomChar();
}
std::cout << "i:" << foo.record.i
<< "\nc:" << foo.record.c
<< "\nf:" << foo.record.f
<< "\nd:" << foo.record.d;
}
See it live!
Technically, this is Undefined Behavior. In practice, it is well defined in most compilers.
I need pi (3.1415...) in arbitrary (but fixed) precision in boost::multiprecision.
The constants in boost::math::constants are only defined up to a fixed number of digits, as pointed out in this answer, so I need to compute it by myself.
Because I'm using this number often and with a very large number of digits, I would like to compute it in runtime only once. what would be a simple yet fast way to have it?
I thought using
typedef number<cpp_dec_float<PRECISION> > mpfloat; // PRECISION is compile time.
const int PI = atan(mpfloat(1))*4;
but I'm not sure this is a common idiom for it.
In c++14 you can use a template variable (http://en.cppreference.com/w/cpp/language/variable_template).
Note that you can already have what you want by including
#include <boost/multiprecision/detail/default_ops.hpp>
That header ends up including constants.hpp which defines template <class T> const T& get_constant_pi().
This is the c++03 idiom for template variables already (as it stores a function-local static result value).
calc_pi has the first 1100 digits hardcoded, and the rest is calculated via optimized formulae if required.
Demo with 50 and 5000 digits:
Live On Coliru (c++14)
#include <boost/multiprecision/cpp_dec_float.hpp>
#include <boost/multiprecision/detail/default_ops.hpp>
#include <boost/multiprecision/number.hpp>
#include <iostream>
namespace {
namespace bmp = boost::multiprecision;
template <int N> bmp::number<bmp::cpp_dec_float<N> > const my_const_pi
= bmp::default_ops::get_constant_pi<bmp::cpp_dec_float<N> >();
}
int main() {
std::cout << std::setprecision(50) << my_const_pi<50> << "\n";
std::cout << std::setprecision(5000) << my_const_pi<5000> << "\n";
}
Prints
3.1415926535897932384626433832795028841971693993751
3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679821480865132823066470938446095505822317253594081284811174502841027019385211055596446229489549303819644288109756659334461284756482337867831652712019091456485669234603486104543266482133936072602491412737245870066063155881748815209209628292540917153643678925903600113305305488204665213841469519415116094330572703657595919530921861173819326117931051185480744623799627495673518857527248912279381830119491298336733624406566430860213949463952247371907021798609437027705392171762931767523846748184676694051320005681271452635608277857713427577896091736371787214684409012249534301465495853710507922796892589235420199561121290219608640344181598136297747713099605187072113499999983729780499510597317328160963185950244594553469083026425223082533446850352619311881710100031378387528865875332083814206171776691473035982534904287554687311595628638823537875937519577818577805321712268066130019278766111959092164201989380952572010654858632788659361533818279682303019520353018529689957736225994138912497217752834791315155748572424541506959508295331168617278558890750983817546374649393192550604009277016711390098488240128583616035637076601047101819429555961989467678374494482553797747268471040475346462080466842590694912933136770289891521047521620569660240580381501935112533824300355876402474964732639141992726042699227967823547816360093417216412199245863150302861829745557067498385054945885869269956909272107975093029553211653449872027559602364806654991198818347977535663698074265425278625518184175746728909777727938000816470600161452491921732172147723501414419735685481613611573525521334757418494684385233239073941433345477624168625189835694855620992192221842725502542568876717904946016534668049886272327917860857843838279679766814541009538837863609506800642251252051173929848960841284886269456042419652850222106611863067442786220391949450471237137869609563643719172874677646575739624138908658326459958133904780275900994657640789512694683983525957098258226205224894077267194782684826014769909026401363944374553050682034962524517493996514314298091906592509372216964615157098583874105978859597729754989301617539284681382686838689427741559918559252459539594310499725246808459872736446958486538367362226260991246080512438843904512441365497627807977156914359977001296160894416948685558484063534220722258284886481584560285060168427394522674676788952521385225499546667278239864565961163548862305774564980355936345681743241125150760694794510965960940252288797108931456691368672287489405601015033086179286809208747609178249385890097149096759852613655497818931297848216829989487226588048575640142704775551323796414515237462343645428584447952658678210511413547357395231134271661021359695362314429524849371871101457654035902799344037420073105785390621983874478084784896833214457138687519435064302184531910484810053706146806749192781911979399520614196634287544406437451237181921799983910159195618146751426912397489409071864942319615679452080951465502252316038819301420937621378559566389377870830390697920773467221825625996615014215030680384477345492026054146659252014974428507325186660021324340881907104863317346496514539057962685610055081066587969981635747363840525714591028970641401109712062804390397595156771577004203378699360072305587631763594218731251471205329281918261861258673215791984148488291644706095752706957220917567116722910981690915280173506712748583222871835209353965725121083579151369882091444210067510334671103141267111369908658516398315019701651511685171437657618351556508849099898599823873455283316355076479185358932261854896321329330898570642046752590709154814165498594616371802709819943099244889575712828905923233260972997120844335732654893823911932597463667305836041428138830320382490375898524374417029132765618093773444030707469211201913020330380197621101100449293215160842444859637669838952286847831235526582131449576857262433441893039686426243410773226978028073189154411010446823252716201052652272111660396665573092547110557853763466820653109896526918620564769312570586356620185581007293606598764861179104533488503461136576867532494416680396265797877185560845529654126654085306143444318586769751456614068007002378776591344017127494704205622305389945613140711270004078547332699390814546646458807972708266830634328587856983052358089330657574067954571637752542021149557615814002501262285941302164715509792592309907965473761255176567513575178296664547791745011299614890304639947132962107340437518957359614589019389713111790429782856475032031986915140287080859904801094121472213179476477726224142548545403321571853061422881375850430633217518297986622371721591607716692547487389866549494501146540628433663937900397692656721463853067360965712091807638327166416274888800786925602902284721040317211860820419000422966171196377921337575114959501566049631862947265473642523081770367515906735023507283540567040386743513622224771589150495309844489333096340878076932599397805419341447377441842631298608099888687413260472
I'd recommend just putting the value of pi into your source code as a constant with however many digits you need.
Define it as a static within a struct.
recently I get to know about a special function in c++ : __gcd(A,B). this will return the greatest common divisor of A and B.
#include<iostream>
#include<algorithm>
using namespace std;
main()
{
cout<<__gcd(10,40); //op: 10
}
is there any special reason for starting function definition with 2 underscores?
It could be as simple as gcd(A,B) like other STL functions.
Names starting with two underscores are reserved for the implementation, which means that you are not allowed to define such names in your code, and there are no standard guarantees what those names mean if they do exist. However, a vendor might choose to document some such names, in which case you can use them with the product for which the vendor documents them.
In C++17 there are standard library functions for GCD and LCM.
#include <iostream>
#include <numeric>
int main ()
{
int a, b;
std::cin >> a >> b;
std::cout << std::gcd(a,b) << '\n';
return (0);
}
I'm studing structures, in the fallowing code my teacher created a structure of the complex numbers (numbers that are formed by two parts: a real one and an imaginary one).
#include <iostream>
#include <cmath>
#ifndef COMPLEX_DATA_H
#define COMPLEX_DATA_H
struct complex_data
{
double re = 0; // real part
double im = 0; // immaginary part
};
#endif
int main()
{
std::cout << "Insert two complex numbers (re, im): ";
complex_data z1, z2;
std::cin >> z1.re >> z1.im;
std::cin >> z2.re >> z2.im;
... // the code continues
}
I'd like to ask two questions:
Leaving z1 and z2 uninitialized will cause any trouble considering they're inside a function and their default inizialitation is undefined?
How can we write the actual form of a variable that is a complex number?
In reality is something like this c = 3 + 2i.
But if we write it, the computer will sum it because it don't know the difference between real numbers and imaginary ones. So we'll be forced to use a string, but in this case it'll become a sequence of charcaters! Any idea?
Using Ubuntu 14.04, g++ 4.9.2.
Since C++11, you have User defined literal (and since C++14 you have the standard literal operator ""i for the pure imaginary number of std::complex<double>).
You may write your own operator ""_i for your custom struct complex_data and also operator + to have what you expect, something like:
constexpr complex_data operator"" _i(unsigned long long d)
{ return complex_data{ 0.0, static_cast<double>(d) }; }
Live example.
Q1- Constructors are meant to intialize the member variables use them.
Q2- Actual Form can be written using strings its just matter of displaying.
c = 3 + 2i.
Compiler really dont know this, you can overload + operarator.
if you define + operator addition will be performed. (whatever code is written in that function e.g real+= a.real;)