if语句c ++中的逻辑运算符[关闭]

Question

底部的当前代码有效，但如果不将 ascii 值移动到我不希望它们出现的位置，我无法组合 if 语句。加密应该只是字母值。大写和小写的 z 应该循环到 A。我有一位老师，但她不知道，所以我会很感激任何帮助。谢谢

这行不通……

if (sentence[i] == 'z' || 'Z')
{
sentence[i] = sentence[i] - 26;
}

这不起作用

if (sentence[i] == 'z' || sentence[i] == 'Z')
{
sentence[i] = sentence[i] - 26;
}

这行得通。

if (sentence[i] == 'z')
{
sentence[i] = sentence[i] - 26;
}
if (sentence[i] == 'Z')
{
sentence[i] = sentence[i] - 26;
}

完整代码。

#include <iostream>
#include <string>

using namespace std;

class EncryptionClass
{
    string sentence;

public:

    //constructors
    EncryptionClass(string sentence)
        {setString(sentence);}
    EncryptionClass()
        {sentence = "";}

    //get and set
    string getString()
        {return sentence;}
    void setString(string sentence)
        {this-> sentence = sentence;}

    //encrypt
    void encryptString()
    {
        for(int i = 0; i < sentence.length(); i++)
        {
            if (isalpha(sentence[i]))
            {

                if (sentence[i] == 'z')
                {
                    sentence[i] = sentence[i] - 26;
                }
                if (sentence[i] == 'Z')
                {
                    sentence[i] = sentence[i] - 26;
                }

                sentence[i] = sentence[i] + 1;
            }
        }
    }
};

int main()
{
    string sentence;
    cout << "Enter a sentence to be encrypted. ";
    getline(cin, sentence);
    cout << endl;

    EncryptionClass sentence1(sentence);
    cout << "Unencrypted sentence." << endl;
    cout << sentence1.getString() << endl << endl;
    sentence1.encryptString();
    cout << "Encrypted sentence." << endl;
    cout << sentence1.getString() << endl;


    cin.get();
    return 0;
}

Answer 1

在您的情况下，两个 If 语句都应该相等。

if (sentence[i] == 'z' || sentence[i] == 'Z')
{
    sentence[i] = sentence[i] - 26;
}

还有：

if (sentence[i] == 'z')
{
    sentence[i] = sentence[i] - 26;
}
if (sentence[i] == 'Z')
{
    sentence[i] = sentence[i] - 26;
}

情况并非总是如此。

片段 2：如果您更改 i 或 sentence[i] 的值，则第二个 if 的行为会有所不同。 如果你将值递减 32，那么两个 sn-ps 的行为将不同

char myChar = 'z'
if (myChar == 'z' || myChar == 'Z')
{
    myChar = myChar - 32;
}
// myChar is now 'Z'

还有：

char myChar = 'z'
if (myChar == 'z')
{
    myChar = myChar - 32;
}
// myChar is now 'Z'
if (myChar == 'Z')
{
    myChar = myChar - 32;
}
// myChar is now ':' 

Answer 2

问题是你应该从你的价值中扣除 25，而不是 26！那是因为字母表中有26个字母，相对编号从0到25（含）。要从最后一个字母（数字25）得到第一个字母（数字0），您需要减去25。

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

但是除了第一个版本之外的每个版本都应该给出相同的结果。

#include <iostream>

int main()
{
    char sentance[] = "Zz";

    for(int i = 0; i < 2; ++i)
    {
        if(sentance[i] == 'Z' || sentance[i] == 'z')
        {
            sentance[i] = sentance[i] - 25;
            std::cout << "letter " << i << " = " << sentance[i] << '\n';
        }
    }
}

Run it here