Controlling how numeric data is stored

You might want to control the format for any of several reasons such as these:

• Arithmetic performed with computational data types is more efficient than with USAGE DISPLAY or USAGE NATIONAL data types.
• Packed-decimal format requires less storage per digit than USAGE DISPLAY or USAGE NATIONAL data types.
• Packed-decimal format converts to and from DISPLAY or NATIONAL format more efficiently than binary format does.
• Floating-point format is well suited for arithmetic operands and results with widely varying scale, while maintaining the maximal number of significant digits.
• You might need to preserve data formats when you move data from one machine to another.

The numeric data you use in your program will have one of the following formats available with COBOL:

• External decimal (USAGE DISPLAY or USAGE NATIONAL)
• External floating point (USAGE DISPLAY or USAGE NATIONAL)
• Internal decimal (USAGE PACKED-DECIMAL)
• Binary (USAGE BINARY)
• Native binary (USAGE COMP-5)
• Internal floating point (USAGE COMP-1 or USAGE COMP-2)

COMP and COMP-4 are synonymous with BINARY, and COMP-3 is synonymous with PACKED-DECIMAL.

The compiler converts displayable numbers to the internal representation of their numeric values before using them in arithmetic operations. Therefore it is often more efficient if you define data items as BINARY or PACKED-DECIMAL than as DISPLAY or NATIONAL. For example:

05  Initial-count   Pic S9(4)  Usage Binary   Value 1000.

Regardless of which USAGE clause you use to control the internal representation of a value, you use the same PICTURE clause conventions and decimal value in the VALUE clause (except for internal floating-point data, for which you cannot use a PICTURE clause).

Examples: numeric data and internal representation