Learn C language with Peng brother

1. Learned three ways to exchange 2 integer variables, the first is to define a variable to act as the existence of an empty bottle, the second is to exchange by addition and subtraction, and the third is to press (binary) Bit XOR, the same is 0, and the difference is 1.
2. Learned to write a piece of code to find a single number in an array, for example int arr[] = {1, 2, 3, 4, 5, 1, 2, 3, 4 }; So 5 is a single number, we commonly call it a single dog
3. Write a shutdown program