You know what an integer is, right? A constant is a quantity that cannot be changed during the running of a program, such as the length of an array (of course, it can be changed during dynamic allocation).

# Define a 100

All subsequent A's will be compiled into100 at compile time;

And the computer will judge whether this constant appears on the left side of the equal sign, and if it does, it will be judged as an error.

Integer variables are variables that can be changed relative to constants and can be assigned values during operation;

Integer expressions are like expressions such as A+B -4+8.