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By Ourusoff N.

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Extra resources for Introduction to Jackson design method.JSP and a little JSD

Example text

Suppose we have a file, F, consisting of two records, T1 and T2. It can be processed by a program with the structure below6: 6 Adapted from Jackson [1], pp. 52-54. 34 P seq P1 seq read; processT1; P1 end P2 seq read; processT2; P2 end P end Here we have allocated the read operations at the start of each component that processes a record. Suppose our file specification changes so that we may or may not have a T1 record at the start of the file, but will always have a T2 record. The data structure is thus: File Possible T1 T1 T2 ° Since only the specification for the part that processes a T1 record has been changed, one would suppose we could modify our program by changing only the P1 component.

So, in a higher-level read operation using both operations, we must assign f^ and then advance the file buffer variable. If we record the status of end-of-file before the file buffer variable is advanced, then we can be assured of processing the current value assigned to n, and avoid the difficulties noted in the schema using the standard Pascal read procedure. We redefine the read procedure below: type intfile = file of integer; var eofbit: boolean; ... g. "read", but before the file buffer variable has been advanced.

88 IN-EOF VALUE 'E'. PROCEDURE DIVISION. PROCFILE. OPEN INFILE. READ INFILE AT END MOVE 'E' TO IN-EOF. MOVE ZERO TO SUM. GE. 0)). DISPLAY "SUM =", SUM. CLOSE INFILE. STOP RUN. COMPUTE-SUM. 43 ADD N TO SUM GIVING SUM. READ INFILE AT END MOVE 'E' TO IN-EOF. 2 Pascal file processing: textfiles As another example, let us design a program to read a textfile consisting of some text and output each word of the input file as a separate line of output. A word is defined as any sequence of letters and apostrophes.

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Introduction to Jackson design method.JSP and a little JSD by Ourusoff N.


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