lpc2138 problem again

i m getting data from external ADC,now i have to store that data in memory,but confused whether to store in RAM or flash.i also don't know the which register to use. plz help me out.

Flash is usually used for long term storage, so you would normally
store results in ram while you work on them.

so i decided to use flash,than i use the word extern n thn decalare n array na,or is any other way is there

declaring variable as extern would not help you access the flash .
To access the flash area through code, you need to use the IAP feature of the LPC21xx controller that you are using.
read the lpc213x user manual for details.