Biorhythm

This program calculates and displays a 30-day biorhythm analysis for a user-specified start date, computing Physical (23-day), Emotional (28-day), and Intellectual (33-day) cycles using sine functions scaled to a range of ±20. The user enters birth date and start date in month/day/year format, and the program derives the day-count difference to feed into the cycle calculations via GOSUB routines at lines 770–820. The code uses cumulative day-of-year arrays (A() and F(), which are duplicated and identical) to convert calendar dates to Julian-style day numbers with the formula at lines 830–840. Several notable anomalies are present: the Intellectual cycle at line 770 correctly uses period 33, but the Physical cycle at line 810 incorrectly uses period 28 (same as Emotional), and the sort/print loop for plotting biorhythm positions on screen (lines 1470–1650) contains control-flow bugs that prevent correct column-ordered output. Summary statistics at line 2510–2530 report total days, hours, and approximate heartbeats since birth before looping back to restart.

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Program Analysis

Program Structure

The program is divided into several logical phases:

1. Initialisation (lines 10–430): Arrays and strings are set up — cumulative day-of-year offsets in A() and F(), month name strings in M$(), and day-name strings in X$() and D$().
2. User input (lines 440–740): Prompts for analysis duration (ZA), start date (M, D, Y), birth date (MB, DB, YB), and user name (A$).
3. Date calculation (lines 830–870): Converts calendar dates to a linear day count (T and TB); computes the age in days (X = T - TB).
4. Header printing (lines 1120–1310): Prints title, start date, birth date, and cycle legend.
5. Main biorhythm loop (lines 1350–1940): For each day, calls GOSUB routines to compute cycle values, attempts to sort positions for tabular output, and advances the date.
6. Closing summary (lines 2500–2560): Displays total days, hours, and estimated heartbeats since birth, then restarts.

Cycle Calculation Subroutines

Three GOSUB routines compute biorhythm values as integers in the range −20 to +20:

Line	Variable	Cycle	Period used	Correct period
770	NI	Intellectual	33	33 ✓
790	NE	Emotional	28	28 ✓
810	NP	Physical	28	23 ✗

The Physical cycle subroutine at line 810 uses a period of 28 days instead of the correct 23, making it identical to the Emotional cycle. This is a straightforward copy-paste bug.

Date-to-Day Conversion

Lines 830–840 use a compact formula to convert a calendar date to a sequential day number:

T = INT(D + 365.25*Y + A(M) + 0.01*M - 0.01)

The 365.25*Y term approximates leap years; the small 0.01*M and offset corrections fine-tune month boundary alignment. The cumulative day-of-year array A() stores the day number at which each month begins (January=0, February=31, etc.). Notably, array F() is initialised to identical values at lines 290–400 but is later reused as a column-position array for the print loop — a recycling of an array name that may cause confusion.

Day-of-Week Calculation

Lines 870 and 1150 compute the day of the week for the birth date and start date respectively:

RB = TB - 1 - INT((TB-1)/7)*7

This is a modulo-7 operation yielding a value 0–6, used to index into X$() and D$() for full and abbreviated day names.

Column Sort and Print Loop — Key Bugs

Lines 1470–1650 attempt to sort the four plot positions (F(1)–F(4) for median, I, E, P markers) into left-to-right screen order, then print them with TAB. Several serious bugs prevent correct operation:

• The inner sort loop (lines 1490–1600) jumps to GOTO 1600 on the true branch of line 1490, skipping the swap at lines 1530–1580 entirely — the sort never executes a swap.
• Line 1500 sets F(I)=0 and clears F$(I) when two positions are equal, but also falls through incorrectly due to missing GOTO.
• The print loop at lines 1620–1650 prints TAB(F(I)) and TAB(F(J)), but J is the inner loop variable left over from the sort loop (value 4 after exit), not an independent iterator — so only F(J) with J=4 is printed on every iteration.

Date Advancement Logic

Lines 1700–1920 advance the date by one day, handling month-end rollovers. However the structure has significant flow issues:

• Line 1720 checks IF M=40 (never true for a valid month) alongside correct 30-day month checks using RM (which is initialised to 0 and never updated, so the condition RM=60 etc. is also always false).
• Lines 1740 and 1760 handle February leap-year and non-leap-year cases but are only reachable if the preceding IF at 1720 does not branch — since the branch target is 1800, these lines are effectively dead code; the program always reaches 1780 and sets L=31.
• The variable RH is used at line 1690 (LET R=RH) but is never assigned after line 59 initialises it to 0, so the day-of-week display never advances.

Duplicate Array Initialisation

Arrays A() (lines 60–160) and F() (lines 290–400) are initialised to exactly the same cumulative day-of-year values. The loop at lines 410–430 iterates over A(I) but merely assigns each element to the scalar A, discarding every value — it performs no useful work. The same applies to the loops at lines 950–970 and 1050–1110 for X$() and M$().

Closing Summary

After the loop completes, lines 2510–2530 print motivational statistics. Note that X at this point has been incremented by 0.5 each half-iteration (line 1660), so the expression X-1 will not equal the integer day count. The heartbeat estimate uses XS*24*90 — approximately 90 beats per minute is reasonable but the factor should be *60*60*24*~70 beats/day; the formula as written gives beats per hour rather than total beats.

Notable Idioms and Observations

• INT(M), INT(D), INT(Y) at lines 610–630 guard against fractional input values.
• The sub-day half-step iteration at line 1660 (LET X=X+.5) with the guard at 1670 (IF INT(X)<>X THEN GOTO 1360) is an attempt to interpolate between days for smoother sine calculation, but since the print routine is re-entered at 1350 on the half-step, it effectively doubles the output rows.
• Line 1180 contains a malformed PRINT statement: "M$(M)STR$ (D)" is a string literal rather than evaluated expressions, so the starting date is never actually printed correctly.
• Line 1260 prints STR$(64) and the literal (35) — this appears to be an attempt to print a divider line but produces the string "64" followed by 35.