Complex number multiplication

[gkn06]

i am trying program based on digital signal processing...i wanna create a function which uses complex type to calculate the vale for cos 2*PI*n/8-j sin 2*PI*n/8..where n=0to2 and i wanna use this function to multiply with scalar....i tried by googling it..but i am totally confused....am getting error such that no match call...

[Aceix]

Try checking the <cmath> header. Useful functions are provided there for you.
http://cplusplus.com/reference/clibrary/cmath/

[gkn06]

i used both <cmath> and <complex>...problem is that operation must define under a function and the function must be multiplied to a real no...i cant do this...anyone pls help me..

[Cubbi]

The complex numbers in C++ have no problem being multiplied by a scalar, as long as the scalar has the same type: complex<double> can be multiplied by a double, but not by an int or even float.

#include <complex>
#include <cmath>
#include <iostream>

const double pi = std::acos(-1);
std::complex<double> f(int n)
{
    return std::complex<double>(
        std::cos(2*pi*n/8), -std::sin(2*pi*n/8)
    );
}

int main()
{
    std::cout << 1.0 * f(0) << '\n'
              << 1.1 * f(1) << '\n'
              << double(10) * f(2) << '\n';
}

[JLBorges]

> complex<double> can be multiplied by a double, but not by an int or even float.

If such a facility is absolutely required:

#include <complex>
#include <type_traits>

template< typename T, typename SCALAR > inline
typename std::enable_if< !std::is_same<T,SCALAR>::value, std::complex<T> >::type
operator* ( const std::complex<T>& c, SCALAR n ) { return c * T(n) ; }

template< typename T, typename SCALAR > inline
typename std::enable_if< !std::is_same<T,SCALAR>::value, std::complex<T> >::type
operator* ( SCALAR n, const std::complex<T>& c ) { return T(n) * c ; }

// and so on for other arithmetic operators

int main()
{
    std::complex<double> c( 1.7, 2.8 ) ;
    auto a = c * 3 ;
    auto b = 2.6f * c ;
    c *= 23 ;
}

[gkn06]

@Cubbi::Thank u very much...i got it....
@JLBorges:how to use this template....

[JLBorges]

> how to use this template....

#include <type_traits> and then just define the template.

Note: with g++ or clang, you also need a compiler option --std=c++11 or (in older versions) --std=c++0x

[gkn06]

there is an output error...in this function cos(2*pi*n/8) when n=2 i must get result as zero...but am getting -1.79821e-006....how to clear this problem...