Can i use a mcd23008 with LCD?
Yes you can use the MCP23008 I2C expander with a character LCD. The hd44780 library actully supports the use of MCP23008 to interface with character LCDs with the hd44780 controller (1602 or 2004 type LCDs).
The library is available in the Library Manager. Go to Library Manager (in the IDE menus, Sketch, Include Libraries, Manage Libraries) and in the Topics dropdown choose Display and in the Filter your search box enter hd44780. Select and install the hd44780 library by Bill Perry.
The class that you want to use is the hd44780_I2Cexp class. There are examples to show how to use the library. The nice thing about the hd44780 library is that it will autodetect the I2C address.
The wiring from the hd44780_I2Cexp.h file :
// hd44780_I2Cexp lcd(addr, chiptype, rs,[rw],en,d4,d5,d6,d7,bl,blpol); // hd44780_I2Cexp lcd(0x20, I2Cexp_MCP23008,1,2,3,4,5,6,7,HIGH); // no rw support