Initial data commit

Task/Caesar-cipher/IS-BASIC/caesar-cipher.basic

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+100 PROGRAM "CaesarCi.bas"
+110 STRING M$*254
+120 INPUT PROMPT "String: ":M$
+130 DO
+140   INPUT PROMPT "Key (1-25): ":KEY
+150 LOOP UNTIL KEY>0 AND KEY<26
+160 PRINT "Original message:  ";M$
+170 CALL ENCRYPT(M$,KEY)
+180 PRINT "Encrypted message: ";M$
+190 CALL DECRYPT(M$,KEY)
+200 PRINT "Decrypted message: ";M$
+210 DEF ENCRYPT(REF M$,KEY)
+220   STRING T$*254
+230   LET T$=""
+240   FOR I=1 TO LEN(M$)
+250     SELECT CASE M$(I)
+260     CASE "A" TO "Z"
+270       LET T$=T$&CHR$(65+MOD(ORD(M$(I))-65+KEY,26))
+280     CASE "a" TO "z"
+290       LET T$=T$&CHR$(97+MOD(ORD(M$(I))-97+KEY,26))
+300     CASE ELSE
+310       LET T$=T$&M$(I)
+320     END SELECT
+330   NEXT
+340   LET M$=T$
+350 END DEF
+360 DEF DECRYPT(REF M$,KEY)
+370   STRING T$*254
+380   LET T$=""
+390   FOR I=1 TO LEN(M$)
+400     SELECT CASE M$(I)
+410     CASE "A" TO "Z"
+420       LET T$=T$&CHR$(65+MOD(ORD(M$(I))-39-KEY,26))
+430     CASE "a" TO "z"
+440       LET T$=T$&CHR$(97+MOD(ORD(M$(I))-71-KEY,26))
+450     CASE ELSE
+460       LET T$=T$&M$(I)
+470     END SELECT
+480   NEXT
+490   LET M$=T$
+500 END DEF