Strange number with fn pow

So I have this loan formula K = (S * (P/100/12)) / (1 - (1 + (P/100/12))^(-Y*12)) and I converted to this

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  	double Prots = (P / 100 / 12);
	double Numb = (Y * 12);
	double K = (S * Prots) / std::pow(1 - (1 + Prots), (-Numb));


But the answer comes out really wierd.
For example if we take S=1200, Y=P=2, the K should be around 51.05, but I get 4.22085e-67.
What is wrong?
You haven't shown the declaration of P, Y or S.
If P is an int, you're going to be doing integer division at line 2.
What is the type of P, Y, S?

Edit:
(1 - (1 + (P/100/12))^(-Y*12))   ||: (P/100/12) = A
(1 - (1 + A)^(-Y*12))   ||: (-Y*12) = B
(1 - (1 + A)^B)   ||: (1 + A) = C
(1 - C^B)
(1 - std::pow( C, B ))

but you have:
std::pow( 1 - C, B )

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P, Y, S are all double
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#include <iostream>
#include <cmath>

int main()
{
	double S, P, Y;
}

I also tried with float, but with that, answer changed to 0.
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