Mathematics Notation Question

just move the number in an array and you can address the single digits; the comfort depends on the programming language you use

 

While I think you could use this notation, however mathematicians view modulo as an operator and not a function. Also subscripts in mathematics are used for coordinate indexing or row/column indexing and your notation would be confusing in those situations.

Programming languages tend to define a general purpose method for modulo where the first argument is the number and the second is the base for the modulo operation. Even in log10 some programming languages use log() for base 10 and ln() for natural logs.