strcasestr performs a case-insensitive substring search, returning a zero-based index pointing to beginning of first occurrence of sub or NULL if not found.
An integer zero-based index to first occurrence of sub.
strstr('AbracadabrA','abrA') -> 7 (Found from the eighth character onwards) strcasestr('AbracadabrA','abrA') -> 0 (Found from the beginning of string)