hi I want to use a very larger integer variable to store a value , an unsigned long integer ( 4 bytes unsigned long integer)maybe overflow! how can i deal with this situation?
Exactly as you learned in elementary school, when you got to the numbers above 9: represent them as a string of numbers in smaller types. That's exactly how 4-byte integers are already implemented on this 8-bit CPU for you, by the Keil runtime libraries. For further reading, Knuth vol. 1 should be helpful.