Data commit

Task/24-game/BBC-BASIC/24-game.basic

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+      REM Choose four random digits (1-9) with repetitions allowed:
+      DIM digits%(4), check%(4)
+      FOR choice% = 1 TO 4
+        digits%(choice%) = RND(9)
+      NEXT choice%
+
+      REM Prompt the player:
+      PRINT "Enter an equation (using all of, and only, the single digits ";
+      FOR index% = 1 TO 4
+        PRINT ; digits%(index%) ;
+        IF index%<>4 PRINT " " ;
+      NEXT
+      PRINT ")"
+      PRINT "which evaluates to exactly 24.  Only multiplication (*), division (/),"
+      PRINT "addition (+) & subtraction (-) operations and parentheses are allowed:"
+      INPUT "24 = " equation$
+
+      REPEAT
+
+        REM Check that the correct digits are used:
+        check%() = 0
+        FOR char% = 1 TO LEN(equation$)
+          digit% = INSTR("0123456789", MID$(equation$, char%, 1)) - 1
+          IF digit% >= 0 THEN
+            FOR index% = 1 TO 4
+              IF digit% = digits%(index%) THEN
+                IF NOT check%(index%) check%(index%) = TRUE : EXIT FOR
+              ENDIF
+            NEXT index%
+            IF index% > 4 THEN
+              PRINT "Sorry, you used the illegal digit "; digit%
+              EXIT REPEAT
+            ENDIF
+          ENDIF
+        NEXT char%
+
+        FOR index% = 1 TO 4
+          IF NOT check%(index%) THEN
+            PRINT "Sorry, you failed to use the digit " ; digits%(index%)
+            EXIT REPEAT
+          ENDIF
+        NEXT index%
+
+        REM Check that no pairs of digits are used:
+        FOR pair% = 11 TO 99
+          IF INSTR(equation$, STR$(pair%)) THEN
+            PRINT "Sorry, you may not use a pair of digits "; pair%
+            EXIT REPEAT
+          ENDIF
+        NEXT pair%
+
+        REM Check whether the equation evaluates to 24:
+        ON ERROR LOCAL PRINT "Sorry, there was an error in the equation" : EXIT REPEAT
+        result = EVAL(equation$)
+        RESTORE ERROR
+        IF result = 24 THEN
+          PRINT "Congratulations, you succeeded in the task!"
+        ELSE
+          PRINT "Sorry, your equation evaluated to " ; result " rather than 24!"
+        ENDIF
+
+      UNTIL TRUE
+
+      INPUT '"Play again", answer$
+      IF LEFT$(answer$,1) = "y" OR LEFT$(answer$,1) = "Y" THEN CLS : RUN
+      QUIT