Declaring variable
We need to tell the computer that we're planning to store a number in a variable before you can actually do it. This is called declaring a variable.
To declare a variable, you need to know what kind of information it will store
n(i.e., will it store a number, or a text-string, or something else) and how you plan to refer to the variable (i.e., the variable's name).
Although there are similarities between a person's memory and a computer's memory, there are some pretty big differences. In C++, you need to grab a little piece of the computer's memory before you can use it.