The first two have the same function, and a is a constant integer. The third meaning is that a is a pointer to a constant integer (that is, the integer cannot be modified, but the pointer can). The fourth meaning A is a const pointer, which points to an integer (that is, the integer pointed by the pointer can be modified, but the pointer cannot be modified). The last one indicates that A is a const pointer and points to a constant integer (that is, the integer pointed by the pointer cannot be modified, and neither can the pointer). If the candidate can answer these questions correctly, then he left a good impression on me. By the way, you may ask, even if you don't use the keyword const, it's easy to write a program with the right function, so why do I value the keyword const so much? I also have the following reasons:

The first two have the same function, and a is a constant integer. The third meaning is that a is a pointer to a constant integer (that is, the integer cannot be modified, but the pointer can). The fourth meaning A is a const pointer, which points to an integer (that is, the integer pointed by the pointer can be modified, but the pointer cannot be modified). The last one indicates that A is a const pointer and points to a constant integer (that is, the integer pointed by the pointer cannot be modified, and neither can the pointer). If the candidate can answer these questions correctly, then he left a good impression on me. By the way, you may ask, even if you don't use the keyword const, it's easy to write a program with the right function, so why do I value the keyword const so much? I also have the following reasons:

The function of the keyword const is to convey very useful information to people who read your code. In fact, declaring a parameter as a constant is to tell the user the application purpose of this parameter. If you spend a lot of time cleaning up the rubbish left by others, you will soon learn to appreciate the extra information. (Of course, programmers who know how to use const rarely leave the garbage to others to clean up. )

The function of the keyword const is to convey very useful information to people who read your code. In fact, declaring a parameter as a constant is to tell the user the application purpose of this parameter. If you spend a lot of time cleaning up the rubbish left by others, you will soon learn to appreciate the extra information. (Of course, programmers who know how to use const rarely leave the garbage to others to clean up. )

Using the keyword const may produce more compact code by providing some additional information to the optimizer.

Reasonable use of the keyword const can make the compiler naturally protect those parameters that don't want to be changed and prevent them from being unintentionally modified by the code. In short, this can reduce the occurrence of bugs.