单表置换加密即让原符号与新符号一一对应，进而对用原符号组成的符号串进行加密。
    加密

    1. //加密
    2. int encrypt(string& sentence)
    3. {
    4.     int location;
    5.     string key      = "qazwsxedcrfvtgbyhnujmikolpQAZWSXEDCRFVTGBYHNUJMIKOLP";
    6.     string alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";     //对应的置换单表，可进行修改
    8.     for (int i = 0; i < sentence.length(); i++)
    9.     {
    10.         location = alphabet.find_first_of(sentence[i]);
    12.         if (location != -1)          //非英文字母不加密
    13.         {
    14.             sentence[i] = key[location];
    15.         }
    16.     }
    17.     return 1;
    19. }

    解密

    1. //解密
    3. int decipher(string& sentence)
    4. {
    5.     int location;
    6.     string key      = "qazwsxedcrfvtgbyhnujmikolpQAZWSXEDCRFVTGBYHNUJMIKOLP";
    7.     string alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    8.     for (int i = 0; i < sentence.length(); i++)
    9.     {
    10.         location = key.find_first_of(sentence[i]);
    12.         if (location != -1)
    13.         {
    14.             sentence[i] = alphabet[location];
    15.         }
    16.     }
    17.     return 1;
    18. }

    完整代码

    1. #include<bits/stdc++.h>
    2. using namespace std;
    4. //单表代替密码
    7. //find_first_of()  
    8. //在母串上从指定位置开始查找，
    9. //如果遇到的字符与目标串中任意字符相同，则查找成功，返回该字符的位置。
    10. //若没有,返回-1
    14. //加密
    15. int encrypt(string& sentence)
    16. {
    17.     int location;
    18.     string key      = "qazwsxedcrfvtgbyhnujmikolpQAZWSXEDCRFVTGBYHNUJMIKOLP";
    19.     string alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";     //对应的置换单表，可进行修改
    21.     for (int i = 0; i < sentence.length(); i++)
    22.     {
    23.         location = alphabet.find_first_of(sentence[i]);
    25.         if (location != -1)          //非英文字母不加密
    26.         {
    27.             sentence[i] = key[location];
    28.         }
    29.     }
    30.     return 1;
    32. }
    35. //解密
    37. int decipher(string& sentence)
    38. {
    39.     int location;
    40.     string key      = "qazwsxedcrfvtgbyhnujmikolpQAZWSXEDCRFVTGBYHNUJMIKOLP";
    41.     string alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    42.     for (int i = 0; i < sentence.length(); i++)
    43.     {
    44.         location = key.find_first_of(sentence[i]);
    46.         if (location != -1)
    47.         {
    48.             sentence[i] = alphabet[location];
    49.         }
    50.     }
    51.     return 1;
    52. }
    55. int main()
    56. {
    57.     string sentence;
    58.     //cout << "请输入要加密的文字:" << endl;
    59.     //getline(cin, sentence);
    60.     sentence = " Time waits  for no man !";
    62.     encrypt(sentence);
    63.     cout << "加密后" << endl;
    64.     cout << sentence << endl;
    66.     decipher(sentence);
    67.     cout << "解密后" << endl;
    68.     cout << sentence << endl;
    71. }