What are the rules governing C++ single and double

Question

For example, these variables:

result (double)
a (double)
b (float)
c (float)
d (double)

A simple calculation:

result = a * (b + c) * d

How and when are the types converted and how do I figure out what precision each calculation is performed at?

Answer 1

You have parenthesis delimiting the float adition. So it would do b + c as float + float. Convert this to double for keeping largest precision, then multiply the double values.

However in such case where you want control over conversions, and not guessing: use static_cast<>();