In Computer programming Why is it considered good programming practice to define the number of array items as a constant before declaring the array?

Answer 1

In computer programming, (1) When a number is needed several times in a program, it is good practice to give that number a name. (2) When a name refers to a number that will never change during a run of a program, it is good practice to declare it as a constant before using it.

In most programming languages, we do not define the number of array items as a constant. In many programming languages, it is easy to add items to an array, and an array keeps track of the number of items it holds, which a program can access using something like "array.length" or "array.shape". However, in C and C++ programming, the programmer must define the size of the array at the time it is defined, and the array does not keep track of the number of items it contains. To not define your array would leave the program open to unchecked growth. "Capping" the array with an upper value ensures that, if something goes wrong, you will not crash the application or system. Also, capping the array will make debugging potentially easier. Capping requires using that number in several places, and so (1) tells us it is good practice to give that number a name. Since it is not possible(*) to change the size of an array in C or C++, the number that holds the number of items in the array will never change, and so (2) tells us it is good practice to declare it as a constant. (*) There are a few tricks one can do with malloc() and realloc() that have the same effect as resizing an array, although technically all those tricks merely create a new fixed-size array.