Only c language please

Given a binary string, write an algorithm to find the number of patterns of form 1[0]1 where [O] represents any number of zeroes (minimum requirement is one 0) there should not be any other character except 0 in the [0] sequence. Note that you are not allowed to use any built-in string function. For example: Input Result 1001000 010101 2 Answer: (penalty regime: 0 %)