What Is a Statement?
It is important to realize that although the words "expression" and "statement" can occasionally be used interchangeably, there is a difference between the two. As you have seen, expressions use operators to manipulate data before they evaluate to a single value (with the possible exception of the assignment expressions that also assigns its value). This is great and an essential part of a programming or scripting language, but expressions can't do anything productive by themselves. Statements are the commands that decide what is done with the data that expressions return and, as you will see shortly, what is done with other statements. Expressions, on the other hand, are usually only a part of a statement, as shown in the example:
const MY_CONST = 72/9;
The 72/9 is a sub-expression of the assignment expression, which assigns the outcome of dividing 72 by 9 (the value 8) to the constant MY_CONST. However, the line, as a whole, is considered to be a const statement. It is the const keyword that causes the constant to be created, thereby doing something useful with the data that the expression to its right evaluates to.
Let's study the type of statement that controls other statements.