Using "D" lines in COBOL can help debug and document your programs.
In all of my COBOL programs, I code an additional print file and documenting/debugging statements, such as:
"STRING 'factor 1 = ' FACTOR1 ', factor 2 = ' FACTOR2 ', result = ' RESULTFIELD DELIMITED BY SIZE INTO INFO PERFORM INFO-TRACE" "MOVE 'subprogram XY now being called' TO INFO PERFORM INFO-TRACE" "STRING 'returned from subprogram XY, returncode was ' RETURNCODE DELIMITED BY SIZE INTO INFO" PERFORM INFO-TRACE" and so on. INFO-TRACE is part of copied subroutines and prints the contents of INFO. Additional in each paragraph I code "MOVE paragraph-name TO PARAGRAPH PERFORM PARA-TRACE" PARA-TRACE is another part of copied subroutines to print the Name of the paragraph.To anhance readability the paragraphs are printed at column 1, INFO is printed at column 4.When I test my programs, each of them will print a complete list of all run paragraphs and all of the INFOs I coded, helping to see which decisons the program made, intermediate results and so on. These lists are especially helpful in tests with many subprograms -- each of them generates its own list. All the lines containing these statements I mark with "TRACED" in columns 1-6, and the "USE FOR DEBUGGING" clause is NOT used. After the testing has been done, I change the debug/document statements (including the additional print file and the copied subroutines) using only 1 SEU-command:
"c 'TRACED ' 'TRACE D' 1 7 a" moving the "D" from column 6 to column 7. The next compilation of the program will treat the statements as comments.
If necessary, the statements can again be set in function using the SEU-command "c 'TRACE D' 'TRACED ' 1 7 a" and a new compilation.