Use the trading checkpoint from the previous lesson; there are no new BASIC lines here. A plan can be affordable and still leave the next year precarious. Work through this example before relying on the word “ready”.
Complete source at this checkpoint
10 BORDER 0: PAPER 0: INK 7: CLS
140 RANDOMIZE
200 LET pop=60: LET grain=360: LET land=100: LET yr=1: LET lost=0
210 LET price=6+INT (RND*5)
220 LET trade=0: LET feed=3*pop
230 IF feed>grain THEN LET feed=grain
240 LET plant=land
250 IF plant>2*INT (feed/3) THEN LET plant=2*INT (feed/3)
260 IF plant>grain-feed THEN LET plant=grain-feed
270 GO SUB 2000
300 GO SUB 8000
310 IF k$="q" OR k$="Q" THEN STOP
320 IF k$="r" OR k$="R" THEN GO TO 200
330 IF k$="b" OR k$="B" THEN LET edit=1: GO SUB 6000: GO TO 270
335 IF k$="s" OR k$="S" THEN LET edit=4: GO SUB 6000: GO TO 270
340 IF k$="f" OR k$="F" THEN LET edit=2: GO SUB 6000: GO TO 270
350 IF k$="p" OR k$="P" THEN LET edit=3: GO SUB 6000: GO TO 270
360 IF k$<>" " OR ok=0 THEN GO TO 300
400 LET oldpop=pop: LET oldgrain=grain: LET oldland=land
410 LET land=land+trade: LET grain=left
420 LET deaths=pop-fed: LET lost=lost+deaths: LET pop=fed
430 LET crop=2+INT (RND*4): LET harvest=plant*crop: LET grain=grain+harvest
440 LET newcomers=0
450 IF deaths=0 THEN LET newcomers=INT (pop/20)
460 LET pop=pop+newcomers
470 GO SUB 4000
500 GO SUB 8000
510 IF k$="q" OR k$="Q" THEN STOP
520 IF k$="r" OR k$="R" THEN GO TO 200
530 IF k$<>" " THEN GO TO 500
540 IF yr=10 OR pop=0 THEN GO TO 5000
550 LET yr=yr+1: GO TO 210
2000 LET fed=INT (feed/3)
2010 IF fed>pop THEN LET fed=pop
2020 LET acres=land+trade: LET cost=trade*price: LET left=grain-cost-feed-plant
2030 LET ok=1: LET m$="All fed. Ready for harvest."
2040 IF fed<pop THEN LET m$=STR$ (pop-fed)+" people will starve."
2045 IF feed>3*pop THEN LET m$="Extra food gives no bonus."
2050 IF left<0 THEN LET ok=0: LET m$="Grain short by "+STR$ (-left)
2060 IF plant>2*fed THEN LET ok=0: LET m$="Too few fed workers."
2070 IF plant>acres THEN LET ok=0: LET m$="Planting exceeds your land."
2080 IF acres<0 THEN LET ok=0: LET m$="You cannot sell that much land."
2090 CLS
2100 PRINT AT 0,1; INK 6; BRIGHT 1;"YEARFALL";AT 0,20;"YEAR ";yr
2110 PRINT AT 2,1; INK 5;"PEOPLE ";pop;AT 2,17;"LAND ";land
2120 PRINT AT 3,1; INK 5;"GRAIN ";grain;AT 3,17;"PRICE ";price
2130 PRINT AT 5,1; INK 4;"PLAN";AT 5,17;"AMOUNT";AT 5,25;"COST"
2135 LET buy=0: LET sell=0
2136 IF trade>0 THEN LET buy=trade
2137 IF trade<0 THEN LET sell=-trade
2138 PRINT AT 6,1;"B Buy land";AT 6,17;buy
2140 PRINT AT 7,1;"S Sell land";AT 7,17;sell
2150 PRINT AT 8,1;"F Feed grain";AT 8,17;feed;AT 8,25;feed
2160 PRINT AT 9,1;"P Plant acres";AT 9,17;plant;AT 9,25;plant
2162 IF trade=0 THEN PRINT AT 10,1; INK 6;"No land bought or sold."
2164 IF trade>0 THEN PRINT AT 10,1; INK 6;"Spend ";cost;" grain on land."
2166 IF trade<0 THEN PRINT AT 10,1; INK 6;"Receive ";-cost;" grain for land."
2170 PRINT AT 11,1; INK 6;"Grain left: ";left
2180 PRINT AT 12,1;"Food needed: ";3*pop
2190 PRINT AT 13,1;"Land after trade: ";acres
2200 PRINT AT 14,1;"Fed workers can plant: ";2*fed
2210 PRINT AT 16,1; INK 6;m$
2220 IF ok=1 THEN PRINT AT 17,1;"After harvest: ";left+2*plant;" to ";left+5*plant
2230 PRINT AT 19,1; INK 5;"B/S land. F/P food/plant."
2240 PRINT AT 20,1;"SPACE harvest. R reset. Q quit."
2250 RETURN
4000 CLS
4010 PRINT AT 0,1; INK 6; BRIGHT 1;"YEARFALL";AT 0,18;"HARVEST ";yr
4020 PRINT AT 2,1;"Yield: ";crop;" grain per acre"
4030 PRINT AT 4,1; INK 5;"GRAIN ACCOUNT"
4040 PRINT AT 6,1;"At start";AT 6,23;oldgrain
4050 IF cost>=0 THEN PRINT AT 7,1;"Land bought: spent";AT 7,23;cost
4055 IF cost<0 THEN PRINT AT 7,1;"Land sold: received";AT 7,23;-cost
4060 PRINT AT 8,1;"Food spent";AT 8,23;feed
4070 PRINT AT 9,1;"Seed spent";AT 9,23;plant
4080 PRINT AT 10,1;"Harvest added";AT 10,23;harvest
4090 PRINT AT 12,1; INK 6;"Grain in store";AT 12,23;grain
4100 PRINT AT 14,1;"People lost: ";deaths
4110 PRINT AT 15,1;"Newcomers: ";newcomers
4120 PRINT AT 16,1; INK 5;"People ";oldpop;" -> ";pop
4130 PRINT AT 17,1; INK 5;"Land ";oldland;" -> ";land
4140 PRINT AT 19,1;"SPACE continues. R restarts."
4150 PRINT AT 20,1;"Q quits."
4160 RETURN
5000 CLS
5010 PRINT AT 2,10; INK 6; BRIGHT 1;"YEARFALL"
5020 PRINT AT 5,2;"Years completed: ";yr
5030 PRINT AT 7,2;"People: ";pop;" (started at 60)"
5040 PRINT AT 8,2;"Grain: ";grain
5050 PRINT AT 9,2;"Land: ";land
5060 PRINT AT 11,2;"People lost over run: ";lost
5070 LET m$="A settlement still standing."
5080 IF lost=0 THEN LET m$="Nobody has starved."
5090 IF lost=0 AND grain>=3*pop THEN LET m$="Growing, with grain in reserve."
5100 IF pop=0 THEN LET m$="The settlement is empty."
5110 PRINT AT 14,1; INK 6;m$
5120 IF pop>0 THEN PRINT AT 16,2;"Next year's food: ";3*pop
5130 PRINT AT 19,1;"R new settlement. Q quits."
5140 GO SUB 8000
5150 IF k$="q" OR k$="Q" THEN STOP
5160 IF k$="r" OR k$="R" THEN GO TO 200
5170 GO TO 5140
6000 LET d$="": LET a$="Buy acres"
6005 IF edit=4 THEN LET a$="Sell acres"
6010 IF edit=2 THEN LET a$="Feed grain"
6020 IF edit=3 THEN LET a$="Plant acres"
6030 PRINT AT 19,0;" ";AT 20,0;" ";AT 21,0;" "
6040 PRINT AT 19,1; INK 6;a$;": ";d$;"_ "
6050 PRINT AT 20,1;"Digits, ENTER. DELETE erases."
6060 PRINT AT 21,1;"X cancels. Blank keeps plan."
6070 GO SUB 8000
6080 IF k$="x" OR k$="X" THEN RETURN
6090 IF CODE k$=13 AND d$="" THEN RETURN
6100 IF CODE k$=13 THEN GO TO 6200
6110 IF CODE k$=12 AND LEN d$>0 THEN LET d$=d$( TO LEN d$-1): GO TO 6040
6130 IF CODE k$<48 OR CODE k$>57 THEN GO TO 6070
6140 IF LEN d$>=4 THEN GO TO 6070
6170 LET d$=d$+k$: GO TO 6040
6200 LET value=VAL d$
6210 IF edit=1 THEN LET trade=value
6215 IF edit=4 THEN LET trade=-value
6220 IF edit=2 THEN LET feed=value
6230 IF edit=3 THEN LET plant=value
6240 RETURN
8000 IF INKEY$<>"" THEN GO TO 8000
8010 LET k$=INKEY$
8020 IF k$="" THEN GO TO 8010
8030 RETURNConsider 60 people, 220 grain and 100 acres, with land priced at eight grain per acre. You want to feed everyone and plant the land. Food costs 180 and planting 100 costs another 100: the plan is short by 60.
A sale changes two sides of the budget
Selling one acre brings in eight grain and, if you plant all remaining land, saves one seed grain. Each acre sold closes nine grain of that particular shortfall. Six acres close 54, which is insufficient. Seven close 63.
| Item | Grain |
|---|---|
| Opening store | 220 |
| Sell seven acres at eight each | +56 |
| Feed sixty people | −180 |
| Plant the remaining ninety-three acres | −93 |
| Reserve before harvest | 3 |
The plan is now valid. A yield of two produces 186 grain, leaving 189. A yield of five produces 465, leaving 468. The display’s possible balance should therefore be 189 to 468.
With no starvation, three newcomers arrive. Next year’s 63 people need exactly 189 grain for food. At the poorest yield, feeding them would leave nothing for seed. Seven acres sold made this year affordable; it did not establish a safe recovery.
Why is selling eight acres not automatically the best answer?
Show the explanation
It leaves twelve grain before harvest and ninety-two planted acres. That gives a slightly larger reserve against the poorest harvest, but permanently removes another acre unless you later buy it back. Its value depends on the next price, harvest and choices. The minimum valid sale and a preferred strategy are different questions.
For a reproducible inspection, quit with Q, then enter LET grain=220, LET price=8 and GO TO 220 as direct commands. This deliberately sets up the example; it is not an ordinary playthrough. Set planting to 100 to see the sixty-grain shortfall. Then sell seven and plant ninety-three. Use R afterwards to restore a normal settlement.
Watch the food requirement, planted area and possible post-harvest balance during play. The program reveals the range, not the next random outcome. Some positions may already be beyond recovery; “ready” only means the current proposal satisfies its rules.
Sources
Steven Vickers, edited by Robin Bradbeer, ZX Spectrum BASIC Programming, second edition (Sinclair Research, 1983), chapter 7.
Run it here
This unit's program, built for you.
- Program
- yearfall.tap
- Machine
- ZX Spectrum 48K (PAL)