a$="THIS IS MY TEXT TO ENCODE WITH CAESAR CIPHER"
Function Cipher$(a$, N) {
      If Len(a$)=0 Then Exit
      a$=Ucase$(a$)
      \\ Integer in Mem is unsigned number
      Buffer Mem as Integer*Len(a$)
      Return Mem, 0:=a$
      For i=0 to Len(a$)-1 {
            If Eval(mem, i)>=65 and Eval(mem, i)<=90 then Return Mem, i:=(Eval(mem, i)-39+n) mod 26 + 65
       }
       =Eval$(Mem)
}
B$=Cipher$(a$, 10)
Print B$
Print Cipher$(B$,-10)

n=1 ' n negative or positive or zero
for i=65 to 65+25
	a=(1+(i -64)+n+24) mod 26 + 65
	? chr$(a),
next