Understanding the essential part from immutable object
In object-oriented programming, we usually manipulate the variable objects many times, even inside the class itself, which we usually describe as the attributes. Also, we sometimes change the global variable from the specific function. However, to gain the immutability feature in functional programming, there are two rules we have to obey. First, we are not allowed to change the local variable. Second, we have to avoid the involvement of the global variable in the function since it will affect the function result.
Modifying a local variable
When we talk about a variable, we are talking about a container to store our data. In our daily programming, we usually reuse the variable we have created. To make it clear, let's take a look at the mutable_1.cpp code. We have the mutableVar variable and store 100 to it. We then manipulate its value for the i variable iteration. The code is written as follows:
/* mutable_1.cpp */
#include <...
