Final answer:
Due to several errors in the code, the function mystery cannot be executed as is. After fixing the errors, if the function were executed, the local variable 'a' within the function would end up with the value 5, but the original variable 'a' in the calling code would remain unchanged.
Step-by-step explanation:
The code snippet provided in the question contains several errors, among which the function name mystery does not match the type signature and variables b and c are incorrectly defined as doubles when they should be integers. Therefore, the original question cannot be executed as is. However, ignoring these errors and assuming the student wants to know the effect of the mystery function on the variable a, we can analyze the function's logic.
The original value of a as a double with a value of -5 would need to be cast to an integer for the mystery function to work. Upon entering the function, since a is negative, we follow the else path. The function then sets flag to true, negates a (which would be -(-5) so a becomes 5), and assigns to c the value of a modulo 2, which in this case is 1. The variable a, which is a local copy inside the function, would end with the value 5, but the original double a in the calling code would remain unchanged because the function accepts an int by value, not by reference or pointer.