can anyone tell the how to write the code for 3 channel ADC and microcontroller interfacing.plz it's very urgent,
Yes.
You pick up all relevant datasheets. You read every single line in the datasheets about the ADC. You read a reasonable amount of the rest of the text in the datasheets, to make sure you are familiar with the (currently unknown) processor and possibly externally connected ADC.
You then take a text editor - most editors should work - and write the source code.
Then it is time to compile the source code - so select a compiler that supports your (currently unknown) processor. When the code is compiled, you may either simulate the system, or download to the (currently unknown) target, and start debugging.
I recommend starting with a single ADC channel, and when that works extend the system. It will depend on your selected system if the extra input is represented by an extra (internally or externally) multiplexed input, or if your (currently unknown) target system will have multiple single-input ADC.
I write this very general text since I realise that your task is so very urgent that you can't be expected to have the time to write a reasonably good description of your problem, and what your target is and your current knowledge level and how much you have managed to currently do on your own.
"You pick up all relevant datasheets. You read every single line in the datasheets about the ADC..."
In addition to the datasheets, be sure to check the manufacturer's website for application notes, design hints, examples, etc, etc...
Also check the examples included with your Keil tools - they're also available in the 'Support' section of this website...