c++ - why type casting doesn't work in here? -

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the following code has type casting error

#define img_i (std::complex<double>(0, 1)) #define pi 3.1415926535 (unsigned long int j = 0; j < 10; ++j)   std::cout << exp(-img_i * pi * j);

the type casting can solved using parenthesis or changing order of multiplication. not clear me why type casting problem occurs in first place , why c++ cannot handle above code is.

can explain me?

this operator* overload std::complex function template declaration looks like:

template<typename t>  complex<t> operator*(const complex<t>& lhs, const t& val);

the t in complex<t> lhs argument must same t val argument in order template argument deduction work.

you trying call std::complex<double> (the type of -img_i * pi) , unsigned long (the type of j). double , unsigned long not same type, template argument deduction fails.

-img_i * (pi * j) works because type of pi * j double, there no ambiguity t is. likewise, -img_i * pi * static_cast<double>(j) works same reason.


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