Boolean

Key Characteristics

• • Simulated Data Type: Unlike many modern programming languages, COBOL and Assembler do not have a native BOOLEAN data type. True/false is represented by specific values in existing data types, such as PIC X fields, single bits, or numeric values.
  • Bit Flags: Often, a single bit within a byte is used as a flag (e.g., 0 for false, 1 for true) to conserve storage, particularly in record layouts or control blocks.
  • Character/Numeric Flags: Common representations include X'00' or 0 for false, and X'01', X'FF', 1, or a specific character like 'Y' for true.
  • Condition Codes (Assembler): The Program Status Word (PSW) in z/Architecture contains condition codes (CC) that are set by various instructions (e.g., COMPARE, ADD) to indicate the outcome, effectively acting as hardware-level boolean flags.
  • Logical Operators: Programs use logical operators (e.g., AND, OR, NOT in COBOL, bitwise operations in Assembler) to combine or negate true/false expressions.

Use Cases

• • Conditional Program Flow: Using IF statements in COBOL or BC (Branch on Condition) instructions in Assembler to execute specific code paths based on whether a condition is true or false.
  • Job Step Execution Control: The COND parameter in JCL allows job steps to be conditionally executed or skipped based on the return codes (boolean success/failure) of preceding steps.
  • Status Indicators: Setting a flag in a record or control block to indicate the success or failure of an operation, the presence of an error, or the state of a resource.
  • Feature Toggles: Using a configuration flag (e.g., in a parameter file or a control field) to enable or disable specific application features or processing options.
  • Data Validation: Evaluating conditions in WHERE clauses in DB2 SQL or IF statements in COBOL to validate input data or filter records based on specific criteria.

Related Concepts