Understanding variables

This is an introduction to variables.

A variable is a program element that can hold volatile data. The following list summarizes variables usage:

• Variables are declared with the DEFINE instruction or with the VAR instruction.
• With the DEFINE instruction, the scope of a variable can be global, local to a module or local to a function.
• With the VAR instruction, the scope of the variable is the code block where the instruction is used, inside a function.
• When defined at the module level, a variable can be declare as PRIVATE or PUBLIC.
• Variables can be defined as records, arrays, dictionaries, etc.
• Variables containing database records are typicaly defined from a database schema with the LIKE clause.
• Variable can be defined from user-types.
• After a definition without initializer, variables get default values specific to their type.
• Default values (or NULL) can be assigned with the INITIALIZE instruction.
• In the definition of a variable, you can specify a value as initializer, for simple and structured types.
• In the code, variable assignment is done with the LET instruction.
• Database validation rules can be applied with the VALIDATE instruction.
• Variables can be used as SQL parameters or fetch buffers in SQL statements.
• Interactive instructions (dialogs) use program variables as model to hold the data.
• Variables can be defined with attributes by using the ATTRIBUTES() clause.