6.2. Using of expressions and variables<br>

## 6.2. Using of expressions and variables

In edition fields, project data described by numerical values can be completed with pre-defined values, values of declared expressions variables or values entered directly by the User.

Values of all numerical fields entered by the User can be given by entering of a number, variable or arithmetical expression.

Values pre-defined in program can be declared directly in edition fields. Then their value is displayed in some fields as “default accepted” for calculations for each new opened project. Such value is for example heat conduction coefficient for the ground. These data should be checked and corrected by the User, depending on project data.

There are also pre-defined values, which are declared in variables editor. Also these values , if need be, should be corrected by the User switching to “Expressions variables”

Values declared in “Expressions variables” can be entered as “default” variables, pre-defined in program or as variables entered by the User. Variables entered by the User are declared by entering the name of variable and ist value in variables editor according to principles described in chapter 4.3.5.

Expressions variables entered as pre-defined are assigned to selected fields and are displayed for each new opened project.

A variable declared by the User is available only in currently edited project. It is not assigned to other projects.

Expressions variables can be used by entering their name in selected data fields. To change the name of value, go back to „Expressions variables” and modify the expression. Change of expression value directly in data edition field will cause disconnecting of declared variable and assigning of entered value. To use this variable once again, just enter its name.

Values entered in edition fields of numerical data can be entered as:

1. Numbers – determining directly the data value,

2. Numerical expression – created by means of mathematical operators on numbers, such as addition „+”, subtraction „-”, multiplication „ * ” and division „ / ”.

3. Expressions variables – declared in project position „Expressions variables”, called in adequate field by entering the name of selected variable. After using the key combination Ctrl + space a list of declared expressions variables will appear.

4. Arithmetical operations on variables and constant numerical values.

5. Functions – called by using the keys combination Ctrl + space. It is also possible to perform mathematical operations on functions.

By means of keys combination Ctrl+space the User can open a list of declared variables and functions. As first will be displayed expressions variables, the unit of which complies with the unit of selected field. Functions are displayed in alphabetical order in a format, which is required to be entered by the User. By means of function the User can determine the area of compartment field, if he knows for example its sector or if he wants the function to adopt its value according to entered function.

Operations on variables must also be contained in required range of values and conformity of variables units being present in expression.

A message „Error” will appear in field, if the User adds variables with different units, for example if he adds m (meter) to a undimensional value.

During multiplication or division of variables a condition for correctness of their input is obtaining of correct unit – conforming to the units system. To enable operations on variables, where one variable is for example undimensional, so called units aliases have been created – the method of their application has been described in chapter 6.3..

It is also possible to declare in program a new variable in any numerical field. This numerical variable can be then used directly by means of keys combination Alt+Ctrl+Insert. In displayed window of variable edition it is necessary to declare its name, value of expression, unit. It is also possible to declare the name setting as a value of variable. That means assigning of numerical value in edition field, entering the declared name of variable.