Mid Range Number

This program calculates the mid-range of a set of numbers entered by the user. It collects values one at a time, tracking the highest and lowest seen so far, and stops when 0 is entered. The mid-range is computed at line 90 as L + ((H−L)/2), which is equivalent to the arithmetic mean of the minimum and maximum values. After displaying the result, the program loops back to line 10 to reset all variables and accept a new dataset. The REM statement at line 5 stores the program title in inverse video characters.

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Program Analysis

Program Structure

The program is organized into three logical phases:

1. Initialization (lines 10–25): Resets all working variables — N (count), M (mid-range result), H (highest value), and L (lowest value) — to zero.
2. Data entry loop (lines 27–80): Prompts the user repeatedly for numbers, updates the running high/low, and exits when 0 is entered.
3. Result and restart (lines 90–130): Computes and displays the mid-range, then jumps back to line 10 to start a fresh session.

Variable Usage

Variable	Purpose
N	Count of numbers entered so far
Z	Most recently entered value
H	Running maximum value
L	Running minimum value
M	Computed mid-range result

Key BASIC Idioms

Lines 55 and 60 use the common idiom of checking IF N=1 to seed both H and L with the first entered value, avoiding a false comparison against the initial zero. This is necessary because valid input could include values less than or equal to zero (though the termination sentinel of 0 complicates such cases — see Bugs section).

The mid-range formula at line 90 uses L+((H-L)/2) rather than the simpler (H+L)/2. Both are mathematically equivalent for real numbers, but the chosen form avoids potential overflow on platforms with limited numeric range — a prudent choice.

Program Flow

The main input loop runs from line 30 back to line 30 via GOTO 30 at line 80. The loop exits at line 40 when Z=0, jumping to the calculation block at line 90. After displaying the result, GOTO 10 at line 130 resets all variables and restarts the program for a new dataset without requiring a manual RUN.

Note that line 45 prints each entered number back to the screen as confirmation, providing a simple running list of inputs.

Notable Techniques

• The title at line 27 is rendered in inverse video using %-escaped characters, making it visually distinct as a heading.
• The REM at line 5 mirrors the title text also in inverse video, serving as an in-listing label.
• A CLS at line 100 clears the screen before the result is shown, giving a clean presentation after potentially many lines of echoed input.

Bugs and Anomalies

• Zero as input: The program uses 0 as a sentinel to terminate input. This means it is impossible to include 0 as a data value in the set being analyzed, which is an undocumented limitation.
• Negative numbers: If the first entered number is negative, H and L are both correctly set to it via the N=1 guards. However, subsequent negative entries will be caught by the Z<L and Z>H checks correctly, so negative data generally works as expected.
• Single value entered: If exactly one number is entered before 0, H and L are both set to that value, so the mid-range correctly returns that value itself.
• No entries before 0: If the user immediately enters 0, H and L remain 0, and the reported mid-range is 0 — a silent edge case with no error or warning message.
• Unreferenced lines: Lines 150 and 160 (SAVE and RUN) are never reached during normal execution; they are utility lines intended to be run manually or as part of a save/autostart workflow.