Please explain to me about this question. I seriously do not understand what this question is asking for. the question is as below:

Write the following function in C.

stripos Find position of first occurrence of a case-insensitive string
int stripos ( char* haystack, char* needle, int offset )

Returns the numeric position of the first occurrence of needle in the haystack string. Note that the needle may be a string of one or more characters. If needle is not found, stripos() will return -1.

The function should not make use of any C library function calls. The code should be developed entirely by you and not extracted from other's work.