Re: sum of 64 bits using 32 bits cpu

sarahh writes:
> 1.I know that the limit of unsigned integer is ~64000

....on a host where unsigned int is 32-bit like on your question, yes....

> what happend in case of overflow it start again from 0.?

Yes.  With 32-bit unsigned int, 0xffffffffU (all bits = 1) + 1U == 0.
Unsigned arithmetic is defined as modulo-(max value + 1) arithmetic.

(Strictly speaking this is not what is called overflow in the C language
- precisely because it is well-defined.  "overflow" is what happens to
signed integers, where the result is not defined.)

> 2.could someone add solution for the question?

The point of homework is to learn by doing.  But if you need a hint:
Think of how you do addition of two-digit numbers by hand, and think
of low and high as the two digits of a number.  (In base 0x100000000
instead of base 10, but what the hey...)  You need to check somehow
whether there was carry from adding the "low" digits.

-- 
Hallvard