Well, the highest bit of int is the sign bit, and the highest bit of unsigned int is the valid bit. In printf, the result is converted to int because %d is used. But in A+B >; When comparing 6, A is unsigned first, and the result is converted into unsigned int. The highest bit of B is 1, which is equivalent to adding a (1

If you don't understand, you can

printf("a+b=%u\n "，(a+b))；

Look at the results.