I like what you did with the '[' and ']' commands, concice and readable. Turning the second if into else if would more likely compile into faster code though.

Can't give a BP upvote though as naming the index position ptr is a bit counter-intuitive, also it seems using int for tape instead of e.g. uint8_t intorduces the need for some awkward modulo ops and prevents the compiler optimizing for space (each "cell" will most likely be much more than the 1 byte required).