Exercise 1: Why Code 35 and Code 47 Represent Genuinely Different Kinds of Problem — Possible Solution ==================================================================== WHAT CATEGORY 3 GENUINELY MEANS, PER THIS CHAPTER'S OWN TABLE This chapter's own real category table states that a first digit of 3 means a permanent error. Code 35 specifically means the file genuinely wasn't found when OPEN INPUT or OPEN I-O was attempted. The real problem here sits outside the program's own control flow entirely - the dataset the program was told to open simply doesn't exist, or isn't reachable, regardless of how correctly the COBOL code itself was written. WHAT CATEGORY 4 GENUINELY MEANS INSTEAD This chapter's own table states that a first digit of 4 means a logic error - specifically, "the file used incorrectly by the program itself." Code 47 means a READ was attempted on a file not genuinely opened for input. This isn't a problem with the external dataset at all; the file may exist and be perfectly readable, but the program's own code made a specific real mistake - trying to read from a file it never opened in a mode that permits reading. WHY THIS IS A GENUINE STRUCTURAL DIFFERENCE, NOT JUST A DIFFERENT NUMBER A code 35 points outward, at the real external environment the program is running in - something about the dataset itself is wrong, and no change to the program's own logic would fix it without also fixing the real external problem (supplying the correct file, for instance). A code 47 points inward, at the program's own source code - the real fix is to correct the program itself, most likely by opening the file in the correct mode before attempting to read it, since the file's own real, external state was never the actual problem. WHY LUMPING BOTH TOGETHER AS "JUST ERRORS" WOULD LOSE SOMETHING REAL Treating every non-zero FILE STATUS the same way - as an undifferentiated "something went wrong" - would obscure this genuinely useful real distinction. Knowing whether a problem is external (fix the environment) or internal (fix the program) is directly actionable information a program's own error-handling logic, or a real person debugging it, can use to decide what to actually do next. ANSWER: Code 35 (category 3, permanent error) means the file genuinely couldn't be found or reached when opened - a real problem with the external environment the program is running in, unrelated to whether the program's own code is correct. Code 47 (category 4, logic error) means the program's own code attempted an operation - reading - that the file's current open mode doesn't support, a genuine mistake in the program itself rather than a problem with the file or dataset. These represent two structurally different kinds of problem because one points outward at the real external environment while the other points inward at the program's own logic - lumping both together as "just errors" would lose the genuinely useful distinction between "fix the environment" and "fix the code." WHY THIS WORKS AS AN ANSWER ------------------------------ This correctly distinguishes an external/environmental failure from an internal/logic failure using this chapter's own category definitions, and explains why that distinction carries real, actionable value rather than treating both codes as interchangeable "errors."