Statistical Analysis System (SAS) Programming Certification Practice Exam

What occurs at the beginning of a DATA step iteration?

1. The automatic variables _N_ and _ERROR_ are incremental by one.

2. The DATA step stops execution.

3. The descriptor portion of the dataset is written.

4. The values of variables created in programming statements are reset to missing.

The correct answer is: The values of variables created in programming statements are reset to missing.

At the beginning of a DATA step iteration, the values of variables created in programming statements are indeed reset to missing. This is an essential aspect of how the DATA step operates in SAS programming. Each time a new iteration of the DATA step begins, the environment is prepared for processing a new observation. This behavior is important for ensuring that variables do not retain values from previous iterations, which could lead to unintended consequences in data processing and analysis. For instance, if the program logic requires different calculations or conditions for each observation, starting with missing values allows for fresh computations without the interference of residual data. The other options represent different stages or aspects of a DATA step's operation. For example, the automatic variables _N_ and _ERROR_ do not increment until the DATA step iteration completes, and the descriptor portion of the dataset is created only once at the beginning of the DATA step, not at the start of each iteration. Similarly, the DATA step continues executing until it reaches an end-point condition, rather than stopping right away. Therefore, the resetting of variable values at the start of each iteration underscores the clear structure and logic in SAS programming, reinforcing data integrity and accurate processing.