1st thing why do u need 4 LDR?
2nd thing why r u using ADC0804?
if you want to get digital output from 4 LDRs then use ADC0809 that has 8 channels.
another option: use micro controller with built in 8 channel ADC like AVR or PIC. ATmega16 is best.
finaly if you want to stick with ADC0804 then use 4x1analog multiplaxer (not digital) before ADC.