How to implement the imaginary part of FFT equation applied to a signal in computer/C++?
In computer programs, complex numbers are usually represented by an array, field or vector containing two values: one value represents the real part, the other represents the imaginary part of the complex number. The imaginary unit itself is usually not represented at all, because this information would be redundant.

An alternative representation is to store the magnitude and phase angle of a complex number.

Specifically in C++, there is the class complex&lt;T&gt; from the STL library that takes care of storing two values of type T for every complex value. You should use that, it's part of the standard libraries.