Here is the simplest possible calculator program, simplified version of bc UNIX utility:
123+456 (unsigned) dec: 579 hex: 0x243 bin: 1001000011 120/10 (unsigned) dec: 12 hex: 0xC bin: 1100 -10 (unsigned) dec: 4294967286 hex: 0xFFFFFFF6 bin: 11111111111111111111111111110110 (signed) dec: -10 hex: -0xA bin: -1010 -10+20 (unsigned) dec: 10 hex: 0xA bin: 1010
It is known that it supports 4 arithmetic operations and negative numbers can be denoted with minus before the number. But it's also known that there are at least 7 undocumented features. Try to find them all.
More challenges: challenges.re; about solutions: challenges.re/#Solutions.