Final answer:
To write the function prototype for Do The Thing, specify it with a constant reference for the read-only float parameter, a reference for the read/write float parameter, and a value parameter for the index with a default value.
Step-by-step explanation:
In computer programming, a function prototype or function interface is a declaration of a function that specifies the function's name and type signature (arity, data types of parameters, and return type), but omits the function body. While a function definition specifies how the function does what it does (the "implementation"), a function prototype merely specifies its interface, i.e. what data types go in and come out of it.
To create a function prototype for Do The Thing that meets the specification provided, the prototype should look as follows: std::string Do The Thing(const float& read Only Float, float& read Write Float, int index = 0); This prototype declares a function that returns a string and takes three parameters. The first parameter is a float, passed by reference, but marked with the const keyword to prevent its value from being changed inside the function.
The second parameter is also a float passed by reference without the const keyword, allowing its value to be modified. Lastly, the integer parameter named index is passed by value with a default value of 0. Declaring a parameter with the const keyword before the type and followed by an & indicates a constant reference, ensuring that the original variable's value cannot be altered by the function.