Final answer:
The 'ref' keyword is used for parameters that are already initialized and can be modified by the method, while 'out' parameters can be uninitialized but must be assigned by the method before it returns.
Step-by-step explanation:
The keywords ref and out are used in C# to pass parameters to methods in a specific way. Both allow a method to modify the value of arguments passed to it, essentially allowing methods to return more than one value.
- ref keyword: When using ref, the data passed has to be initialized before it is passed to the method. This means the variable must have been given a value before it is used in the method call. The method can read and modify the value of a ref parameter.
- out keyword: In contrast, an out parameter does not have to be initialized before being passed to a method. However, the method is required to assign a value to an out parameter before the method returns. This means the method's intent is to provide a result as an output, not to read the incoming value.
In summary, use ref when the method needs to modify an existing variable and use out when the method needs to provide an output that didn't necessarily have an initial value.