Can @ and @@ be used together in the same DATA step?

The correct answer is rooted in understanding how the @ and @@ symbols are used in SAS programming. Both @ and @@ are used for line-hold specifiers in the DATA step, helping manage the way data is read from the input. The single @ holds the input line for the next iteration of the DATA step, while the double @@ keeps the input line for subsequent iterations of the DATA step without advancing to the next input line.

Since they serve different purposes, it is feasible to use both within the same DATA step, allowing for greater flexibility in managing input data. For example, one can use @ to control when to stop reading a certain line while also using @@ to read multiple observations from the same input line. This capability offers a programmer significant control over input data processing, enhancing the functionality of a DATA step when dealing with various input formats.

While using @ and @@ together can offer benefits, the exact context of their use needs to be clearly understood, as improper application can lead to logical errors or unexpected results in data handling. However, the coexistence of both symbols in a single DATA step transaction demonstrates the versatility provided to the programmer.