#### How earlier expressions affect later expressions

The fact that a Crystal syntax formula is a sequence of expressions whose result is the value of the final expression is the most important concept in understanding Crystal syntax. This expression-based syntax allows you to write very short formulas with a lot of functionality.

##### Example

    //First expression. It declares the Number variable x
    //and then returns the value of an uninitialized
    //Number variable, which is 0.
    NumberVar x;
    //Second expression. It assigns the value of 30 to x,
    //and returns 30.
    x := 30

The above formula would give an error if the first expression were omitted. This is because the second expression refers to the Number variable x, and the program needs to have x declared before it understands expressions
involving it.

In general, you use variables to get the earlier expressions in a formula to affect the final expression. See Variables for more information.

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