The definition of a specific problem normally requires the use of numerical (integer or real) data values. Such values can be specified in two ways. Firstly, the values may simply occur as integer or floating-point numbers in data fields 4 and 6. Secondly, values may be allocated to named parameters, known as integer or real parameters, and a value subsequently used by reference to a particular integer or real parameter name. This second method may only be used to allocate values on certain cards; when this facility is used, the first character in field 1 on the relevant data card will be an X or a Z. This latter approach is particularly useful when a value is to be used repeatedly or if a value is to be changed within a do-loop (see Section 3.2.4).
We defer the definition of integer and real parameters until Section 3.2.3.