Your code doesn't return -1 when bounce is 1

If bounce is 1 and h is greater than window, it will always be greater than window so the loop runs forever.

I don't see it either, but since the code uses the nonstandard function strrev(), it's automatically non-portable even without plusDot().

may i know where does plusDot come from?

I got it, thank you!

maybe the equation result should be n > log(window/h) / log(bounce) ? Since bounce < 1, then log(bounce) < 0. So we use ceil here.

The thing is that the width specifiers don't dictate the particular argument length, but only maximum.
So the string with exact same length can have value that doesn't fit the pattern but will be accepted if we remove this check.

may anyone explain the code started from b += c > 1 ? I don't understand why c, which is index, is added to pointer b. This expression will give value of b after assigning, which must be > 1. Also, will this update pointer b and left some memory unused?
Besides, as a terminating null character is automatically appended after the content written in snprintf, how can the code solve this problem?

thx for your reply, but the code has already checked whether strlen(number) == frmt_len, input with incorrect length cannot pass the condition. May anyone explain this to me please?

it is used to catch any extra trailing characters, then sscanf would return 8, and not 7, therefore when it returns exactly 7 we are sure that we don't have any trailing characters.

may i know why %1s is used at the sscanf function? Thank you.