Campbell Scientific CR6 CR6 Measurement and Control System - Page 143
Constants, 8.3.4.3 Alias and Unit Declarations
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Section 7. Installation variables, create a data table to which the local variables are sampled, then display those sampled data. When passing the contents of a global variable to a local variable, or local to global, declare passing / receiving pairs with the same data types and applicable string lengths. 7.8.3.4.2 Constants CRBasic example Using the Const Declaration (p. 143) shows use of the constant declaration. A constant can be declared at the beginning of a program to assign an alphanumeric name to be used in place of a value so the program can refer to the name rather than the value itself. Using a constant in place of a value can make the program easier to read and modify, and more secure against unintended changes. If declared using ConstTable / EndConstTable, constants can be changed while the program is running by using the external keyboard display menu (Configure, Settings | Constant Table) or the C command in a terminal emulator (see Troubleshooting - Terminal Emulator (p. 484) ). Note Using all uppercase for constant names may make them easier to recognize. CRBasic Example 11. Using the Const Declaration ' the use of the Const declaration. 'Declare variables Public PTempC Public PTempF 'Declare constants Const CtoF_Mult = 1.8 Const CtoF_Offset = 32 BeginProg Scan(1,Sec,0,0) PanelTemp(PTempC,250) PTempF = PTempC * CtoF_Mult + CtoF_Offset NextScan EndProg Predefined Constants Many words are reserved for use by CRBasic. These words cannot be used as variable or table names in a program. Predefined constants include instruction names and valid alphanumeric names for instruction parameters. On account the list of predefined constants is long and frequently increases as the operating system is developed, the best course is to compile programs frequently during CRBasic program development. The compiler will catch the use of any reserved words. 7.8.3.4.3 Alias and Unit Declarations A variable can be assigned a second name, or alias, in the CRBasic program. Aliasing is particularly useful when using arrays. Arrays are powerful tools for complex programming, but they place near identical names on multiple variables. 143
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