C ++用户输入限制，具有适当的重试而没有“goto” [英] C++ user input restriction with proper retry without "goto"

问题描述

我有以下代码：

qstn:
  cout << "Input customer's lastname: ";
  getline(cin, lname);

  if (lname.find_first_not_of("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ ") != string::npos) {
      cout << "You can only input alpha here!\n";
      cin.clear();
      goto qstn;
  } else if (lname.empty()) {
      cout << "Please enter your firstname!\n";
      cin.clear();
      goto qstn;
  }

  int lnamel = lname.length();
  int strl = str.length();
  int is = 0;

  for (int i = 1; i < strl;) {
      i++;
      is++;

      if (lname[i] == lname[is] && lname[i] == ' ' || lname[0] == ' ') {
          cin.clear();
          cout << "Please input your lastname properly!\n";
          goto qstn;
      }
  }
  // next question here

m有一个很难的时间在思考什么是正确的逻辑，以避免
goto语句，因为我大学时我正在使用它，但有人在这里说，
不好使用它在所有原因可能毁了我的代码。

I'm having a hard time on thinking what will be the proper logic to avoid the goto statement, since I was college I was using it but someone here said that it's not good to use it at all cause it might ruin my code.

我尝试使用do while循环，但它不像goto一样流畅。

I tried using the do while loop but it's not smooth as goto.

请帮助！

推荐答案

使用函数：

bool getLastName(string & lname,
                 string & str)
{
    cout << "Input customer's lastname: ";
    getline(cin, lname);

    if (lname.find_first_not_of("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ ")
            != string::npos)
    {
        cout << "You can only input alpha here!\n";
        cin.clear();
        return false;
    }
    else if (lname.empty())
    {
        cout << "Please enter your firstname!\n";
        cin.clear();
        return false;
    }
    int lnamel = lname.length();
    int strl = str.length();
    int is = 0;
    for (int i = 1; i < strl;)
    {
        i++;
        is++;
        if (lname[i] == lname[is] && lname[i] == ' ' || lname[0] == ' ')
        {
            cin.clear();
            cout << "Please input your lastname properly!\n";
            return false;
        }
    }
    return true;
}

所有我在这里做的是替换 goto 与 return false 。如果程序使它到函数的结尾， return true 。在while循环中调用函数：

All I've done here is replace the gotos with return false. If the program makes it to the end of the function, return true. Make the function call in a while loop:

while (!getLastName(lname, str))
{
    // do nothing
}

这不仅代码化了代码，但它把它分解成好，小，容易管理的片段。这称为程序编程。

Not only does this de-spaghettify the code, but it breaks it up into nice, small, easy to manage pieces. This is called procedural programming.

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