OPTION BASE 0

FUNCTION IsLeapYear(y) !うるう年の判定
   LET  IsLeapYear=0
   IF (MOD(y,4)=0 AND MOD(y,100)<>0) OR MOD(y,400)=0 THEN
      LET  IsLeapYear=1
   END IF
END FUNCTION

FUNCTION DateFrom111(y,m,d) !西暦１年１月１日から、第何日目
   DIM Month(12)
   LET Month(1)=31
   LET Month(2)=28
   LET Month(3)=31
   LET Month(4)=30
   LET Month(5)=31
   LET Month(6)=30
   LET Month(7)=31
   LET Month(8)=31
   LET Month(9)=30
   LET Month(10)=31
   LET Month(11)=30
   LET Month(12)=31
   LET yy=y-1
   LET aa=yy*365+INT(yy/4)-INT(yy/100)+INT(yy/400)
   FOR i=1 TO m-1
      LET aa=aa+Month(i)
   NEXT i
   IF m>2 THEN LET aa=aa+IsLeapYear(y)
   LET aa=aa+d
   LET DateFrom111=aa
END FUNCTION

SUB Ymd(n,E,S,RM) !西暦第○日の西暦年月日を求める
   DIM Month(13)
   LET Month(0)=31
   LET Month(1)=31
   LET Month(2)=28
   LET Month(3)=31
   LET Month(4)=30
   LET Month(5)=31
   LET Month(6)=30
   LET Month(7)=31
   LET Month(8)=31
   LET Month(9)=30
   LET Month(10)=31
   LET Month(11)=30
   LET Month(12)=31
   LET X=365*4+1
   LET Y=X*24+365*4
   LET Z=Y*4+1
   LET Q=INT(n/Z)
   LET QM=MOD(n,Z)
   LET W=INT(QM/Y)
   LET WM=MOD(QM,Y)
   LET K=INT(WM/X)
   LET KM=MOD(WM,X)
   LET R=INT(KM/365)
   LET RM=MOD(KM,365)
   LET E=400*Q+100*W+4*K+R+1
   LET S=0
   IF (MOD(E,4)=0 AND MOD(E,100)<>0) OR MOD(E,400)=0 THEN
      LET Month(2)=29
      DO WHILE RM=>0
         LET S=S+1
         LET RM=RM-Month(S)
      LOOP
   ELSE
      DO WHILE RM=>0
         LET S=S+1
         LET RM=RM-Month(S)
      LOOP
   END IF
   LET RM=RM+Month(S)
   IF RM=0 THEN
      IF S=1 THEN 
         LET S=12
         LET E=E-1
         LET RM=Month(S)
      ELSEIF (MOD(E,4)=0 AND MOD(E,100)<>0) OR MOD(E,400)=0 AND S=3 THEN
         LET S=2
         LET RM=29 
      ELSE
         LET S=S-1
         LET RM=Month(S)
      END IF
   END IF 
END SUB


DIM Youbi$(7)
DATA 日,月,火,水,木,金,土
FOR i=0 TO 6
   READ Youbi$(i)
NEXT i
PRINT
INPUT PROMPT "基準になる西暦：年, 月, 日？ ":h,f,g
INPUT PROMPT "何日後？ ":a
PRINT
LET b=DateFrom111(h,f,g)
CALL Ymd(b+a,E,S,RM)
LET YOU=MOD(b+a,7)
PRINT "  ";h;"年";f;"月";g;"日 から ";a;"日後は、"
PRINT E;"年";S;"月";RM;"日  ";Youbi$(YOU);"曜日 です。"
PRINT
END