The error you're encountering, "Undefined function or variable 'pd1_2'", occurs because the `case 2` block is never executed. This is due to the fact that the loop only runs once (`data_num = 1`), and thus, the `switch` statement only evaluates `case 1`. As a result, `pd1_2` and `pd2_2` are never defined. Possible workarounds:
- If you intend to execute both cases, increase the `data_num` to at least 2.
- If `case 2` might not always execute, initialize `pd1_2` and `pd2_2` outside the loop to avoid the undefined variable error.
- Before accessing `pd1_2` and `pd2_2`, add a check to ensure they are defined.
