Final answer:
The domain for the given C++ function 'float sum(int x)' is the set of all integers.
Step-by-step explanation:
The domain of a function refers to the set of all possible input values for that function. In this case, the function 'sum' takes an integer value as input and returns a float value as output.
Since there are no restrictions mentioned in the question, we can assume that the domain includes all possible integer values.
Therefore, the domain for the given C++ function 'float sum(int x)' is the set of all integers.