我正在从SICP做练习1.3。
我的代码如下：
#lang racket
(require sicp)
(define (square a)
(* a a)
)
(define (sum-of-squares a b)
(+ (square a) (square b) )
)
(define (max a b)
(cond ((>= a b) a)
(else b)
)
)
(define (sum-of-biggest-squares a b c )
(cond ((>= a b)
(sum-of-squares a (max b c) )
(sum-of-squares b (max a c) )
)
)
)
(sum-of-biggest-squares 5 7 10)
令人惊讶的是，Racket解释器
不打印上述任何结果。口译员
适用于其他值。但是对于
这三个值的集合不是
的工作。
当我尝试添加else语句时
如下：
(else (sum-of-squares b (max a c) ) )
口译员说：
exercise_1-3.rkt:23:10: else: not allowed as an expression
in: (else (sum-of-squares b (max a c)))
答案 0 :(得分：0)
您在函数else中有几个语法错误：应添加一个括号以关闭第一个(define (sum-of-biggest-squares a b c)
(cond ((>= a b) (sum-of-squares a (max b c)))
(else (sum-of-squares b (max a c)))))
子句，并将public class AES256Hash
{
private static byte[] key;
private static Object mutex = new Object();
private const int KEY_SIZE = 256;
private const int BLOCK_SIZE = 128;
private const int IV_KEY_SIZE = 16; // 16 byte
private AES256Hash()
{
}
/// <summary>
/// Create a new randomized cipher on each startup
/// </summary>
private static void InitializeCipherKey()
{
lock (mutex)
{
if (key == null)
{
key = new byte[32];
var cr = new System.Security.Cryptography.RNGCryptoServiceProvider();
cr.GetBytes(key, 0, key.Length);
}
}
}
/// <summary>
/// Converts the input data into an IV key
/// </summary>
/// <param name="Data"></param>
/// <returns></returns>
private static byte[] CreateIvKey(string Data)
{
byte[] IvKey = new UTF8Encoding().GetBytes(Data);
if (IvKey.Length != IV_KEY_SIZE)
{
byte[] NewTruncatedIvKey = new byte[IV_KEY_SIZE];
Buffer.BlockCopy(IvKey, 0, NewTruncatedIvKey, 0, Math.Min(IV_KEY_SIZE, IvKey.Length)); // the rest of the bytes are 0 padded
return NewTruncatedIvKey;
}
return IvKey;
}
/// <summary>
/// Encrypts a string with AES256 with the given key and string data
/// </summary>
/// <param name="Key"></param>
/// <param name="Data"></param>
/// <returns></returns>
public static string EncryptString(string Key, string Data)
{
InitializeCipherKey();
byte[] IvKey = CreateIvKey(Key);
byte[] dataB = new UTF8Encoding().GetBytes(Data);
using (AesCryptoServiceProvider csp = new AesCryptoServiceProvider())
{
csp.Padding = PaddingMode.PKCS7;
csp.Mode = CipherMode.ECB;
csp.KeySize = KEY_SIZE;
csp.BlockSize = BLOCK_SIZE;
csp.Key = key;
csp.IV = IvKey;
ICryptoTransform encrypter = csp.CreateEncryptor();
return Convert.ToBase64String(encrypter.TransformFinalBlock(dataB, 0, dataB.Length));
}
}
/// <summary>
/// Decrypts a string with AES256 with the given key and string data
/// </summary>
/// <param name="Key"></param>
/// <param name="Data"></param>
/// <returns></returns>
public static string DecryptString(string Key, string Data)
{
InitializeCipherKey();
byte[] IvKey = CreateIvKey(Key);
byte[] dataB = Convert.FromBase64String(Data);
using (AesCryptoServiceProvider csp = new AesCryptoServiceProvider())
{
csp.Padding = PaddingMode.PKCS7;
csp.Mode = CipherMode.ECB;
csp.KeySize = KEY_SIZE;
csp.BlockSize = BLOCK_SIZE;
csp.Key = key;
csp.IV = IvKey;
ICryptoTransform decrypter = csp.CreateDecryptor();
return new UTF8Encoding().GetString( decrypter.TransformFinalBlock(dataB, 0, dataB.Length) );
}
}
}
添加到第二个：{{1}}：
{{1}}
请注意，格式化代码的方式与当前的常见约定不同，因此很难读取它并且很容易引入语法错误。