## 2. First Programs

### Expressions, Primary and Compound, and Parentheses

Round brackets, also called parentheses, can be used to group expressions:

```    cout << (3 + (28-2)*5)*2;
```

Should we carry out this statement, we will get the following result:

```STDOUT:

266
```

Before you get any ideas, we should warn you that it is not allowed in C++ to use square brackets to group expressions. It is also not allowed to use curly brackets, also called braces, to group expressions. For example;

```cout << [3 +(28-2)*5]*2;  // INCORRECT
```

Let's now explain the structure of expressions. The simplest kind of an expression is a literal expression. A literal expression is the one stating its value literally. No computation is required to figure out the value of a literal expression.[*]

For example, number 5 is an expression by itself and it is a literal expression. Its value equals 5, obviously. Here is an example:

```int main()
{
cout << "This number is a literal expression: " << 24 << endl;

cout << "This string is a literal expression, too!" << endl;
}
```

It results in:

```STDOUT:

This number is a literal expression: 24
This string is a literal expression, too!

```

As the example says, strings are literal expressions, because the value of a string is literally stated between the quotation marks.

Literals are one kind of primary expressions. An expression is either a primary expression or a compound expression. Compound expressions are created by combining other expressions, or by modifying other expressions with operators. For example, the expression `5 + 2*6` is a compound expression. It is made of the literal expression `5`, the operator `+` and the compound expression `2*6`. In turn, the compound expression `2*6` is made of the literal expression `2`, the multiplication operator and the literal expression `6`.