1000 PRINT "多角形の面積" 1010 DO 1020 PRINT 1030 PRINT "頂点の個数(2 以下の数を入れると終わります)[n] "; 1040 INPUT N 1050 IF N<3 THEN EXIT DO 1060 PRINT "頂点"; 1; " [x,y] "; 1070 INPUT X1,Y1 1080 LET XOld=X1 1090 LET YOld=Y1 1100 LET S=0 1110 FOR K=2 TO N 1120 PRINT "頂点"; K; " [x,y] "; 1130 INPUT XNew,YNew 1140 LET S=S+(XOld-XNew)*(YOld+YNew) 1150 LET XOld=XNew 1160 LET YOld=YNew 1170 NEXT K 1180 LET S=S+(XOld-X1)*(YOld+Y1) 1190 LET S=ABS(S)/2 1200 PRINT "面積は"; S; "です" 1210 LOOP 1220 STOP 1230 END