1. Whether or not to retain the sign bit when the character is extended to the integer type. Some implement to retain the sign bit, and some directly fill the sign bit with 0 at the high level without retaining the sign bit.
2. When the right shift is performed, the value of the blank bit is filled. Some C languages are used to fill 0, while others are used to fill the sign bit.
3. Shift count restrictions. For example, for int type data, it is usually the number of digits not exceeding this type, that is, the shift to int type data cannot exceed 32.
4. The memory location is 0. Some C languages implement hardware-level protection for the 0 memory location and do not allow read/write; some implement read-only; others implement read-only and writable. 5. If (a) Main calls exit or _ exit without termination, or (B) Main executes a return statement without return values, or (c) if an implicit return is executed for main, the termination status of the process is undefined.
