There are two mistakes in this sentence. The first is that variables cannot be enclosed in%% when they are set. If it is enclosed, if there is this value (for example, the original a=99), the code set 99=08 will be generated. The second error, the number starting with 0 is octal and can only contain the numbers 0-7. "8" is illegal, so the definition of A is invalid.

In the set, b=a+ 1. If A does not exist, it defaults to 0, because the assignment of A in the previous step is incorrect, so the calculation of B here is equal to 1.