## Scalar Variables

The GCE module is mostly used to calculate 2D plane geometric objects,
while constraints and dimensions are applied to them. These data types
inherently have vector representation. Parametric drawing assumes that
geometry is linked with driving or variational numeric parameters. So it
is impossible to do without another type, a **numeric variable** or a
**scalar**. Their values are usually expressed using distance or angle
measurement units.

Variables of the following type can only be used in a parametric
constraint system:

-   A numeric variable associated with a dimension, it is a
    **dimensional variable**. When resolved, a dimensional variable is
    equal to measured dimension value. Dimensional variable can be both
    an independent driving parameter of a sketch, or
    variational/measurement parameter. The use of variables for creating
    driving and variational dimensions is discussed in Item [Driving and
    Variational
    Dimensions](../../../TWO-DIMENSIONAL_DIMENSIONS/subsections/EN/Driving_and_Variational_Dimensions.md).

-   An auxiliary geometric constraint parameter, for example, a
    parameter that specifies where tangency points are for complex
    curves. You can find more details in **Auxiliary tangency
    parameter** Section, Item
    [Tangency](../../../TWO-DIMENSIONAL_LOGICAL_CONSTRAINTS/subsections/EN/Tangency.md).

-   A variable that is not associated with a geometric constraint or a
    dimension may be used in scalar linear or non-linear equations that
    establish relations between first values and other values.

In GCE module API, a variable is represented by the var_item data type.
You can create variables by calling

```cpp
var_item GCE_AddVariable(GCE_system gSys, double val).
```

The function returns a descriptor of a scalar variable with the initial
value **val**. The variable with this descriptor can be further used to
determine dimensions, constraints, and equations.

Any variable can be **dependent** or **independent.** A dependent
variable is governed by measurement dimensions or constraints, and its
value is calculated by the solver. An independent variable can't be
modified by the solver, and its value is defined by the application. To
make a variable independent, just call

```cpp
constraint_item GCE_FixVariable(GCE_system gSys, var_item var), 
```

that will create a driving parameter constraint and return the
constraint descriptor that fixes its value. An independent variable can
be varied by calling **GCE_ChangeDrivingDimension**() method. Driving
parameter constraint together with other types of driving dimensions
permits to create a parametric sketch; its geometry can be changed
according to a user defined law by changing independent parameters.
Creation of driving parameters and dimensions is described in Item
[Driving and Variational
Dimensions](../../../TWO-DIMENSIONAL_DIMENSIONS/subsections/EN/Driving_and_Variational_Dimensions.md).