只是一个基本的卡萨密码。我已经测试了所有的子函数,只是 encryptChar() 并不是特别有效。我得到一个无限循环。它应该是递归的。这是所有代码:
fun replace (str : string, index : int, newChar : char) : string = String.substring(str,0,index) ^ String.str(newChar) ^ String.substring(str,index+1,(size str) - index - 1;
fun encryptChar (msgStr : string, shiftAmnt : int, index : int) : string =
let val asciiCode = 0
in
if (not (String.sub(msgStr, index) = #" ")) then
(
asciiCode = ord( String.sub(msgStr, index) ) + shiftAmnt;
if (asciiCode < ord(#"A")) then asciiCode = asciiCode + 26
else if (asciiCode > ord(#"Z")) then asciiCode = asciiCode - 26
else asciiCode = asciiCode;
msgStr = replace(msgStr, index, chr(asciiCode))
)
else asciiCode = asciiCode;
index = index + 1;
if (index < (size msgStr - 1)) then encryptChar(msgStr, shiftAmnt, index)
else msgStr
end
;
fun encrypt(msgStr : string, shiftAmnt : int) : string = encryptChar (String.map Char.toUpper msgStr, shiftAmnt mod 26, 0);