C integer overflow behaviour when assigning to larger-width integers

Question

If I execute the following code in C:

#include 

uint16_t a = 4000;
uint16_t b = 8000;

int32_t c = a - b;

printf(\"%d\", c);

Answer 1

There is, in fact, an overflow but C does not tell you.

The overflow leaves a value that happens to be -4000 when interpreted as a signed integer. This works as designed on 2's complement machines.

Try to interpret the result as unsigned, and you'll notice that (u1-u2) evaluates to some seemingly unrelated number when u1 < u2.