如何在 C# 中使用两个 if 语句？答案

【问题标题】：How to use two if statements in C#?如何在 C# 中使用两个 if 语句？
【发布时间】：2021-12-24 22:25:11
【问题描述】：

这是我的 ATM 代码，但不知何故，当我按数字键盘上的数字 2 时，我得到了我的 else 声明，这个数字别无选择。

Console.WriteLine("What is your name? ");
string userName = Console.ReadLine();
Console.WriteLine("You are: " + userName);
Console.WriteLine("How much money do you have? ");
string Balance = Console.ReadLine();
float startBalance = float.Parse(Balance);

Console.WriteLine(userName + ", your balance is " + startBalance + " EUR");
Console.WriteLine("Press 1 for WITHDRAWAL");
Console.WriteLine("Press 2 for DEPOSIT");


if (Console.ReadKey().Key == ConsoleKey.NumPad1)
{
    Console.ReadLine();
    Console.WriteLine("How much money do you wish to withdraw? ");
    string Withdrawal = Console.ReadLine();
    float wBalance = float.Parse(Withdrawal);

    Console.WriteLine("Your new balance is " + (startBalance - wBalance) + " EUR");
    Console.ReadLine();
    Environment.Exit(0);

} 



if (Console.ReadKey().Key == ConsoleKey.NumPad2)
{
    Console.ReadLine();
    Console.WriteLine("How much money do you wish to deposit? ");
    string Deposit = Console.ReadLine();
    float dBalance = float.Parse(Deposit);

    Console.WriteLine("Your new balance is " + (startBalance - dBalance) + " EUR");
    Console.ReadLine();
    Environment.Exit(0);

}

else Console.WriteLine("There was no choice for this number");

【问题讨论】：

您是否使用调试器逐步完成此操作？
当你有这个代码工作时，把它带到 codereview stackexchange - 这里有很多可以改进的地方，让它更干净。如果你现在养成好习惯，以后会有所帮助。
希望我的银行在给我提款选项之前问我有多少钱！ ????

标签： c# .net if-statement console

【解决方案1】：

您有两个独立的ifs 和两个独立的Console.ReadKey() 调用。

相反，将该调用提取到一个变量中，并使用 if-else if-else 序列对其进行评估：

ConsoleKeyInfo.Key key = onsole.ReadKey().Key;

if (key == ConsoleKey.NumPad1)
{
    Console.ReadLine();
    Console.WriteLine("How much money do you wish to withdraw? ");
    string Withdrawal = Console.ReadLine();
    float wBalance = float.Parse(Withdrawal);

    Console.WriteLine("Your new balance is " + (startBalance - wBalance) + " EUR");
    Console.ReadLine();
    Environment.Exit(0);
} 
else if (key == ConsoleKey.NumPad2)
{
    Console.ReadLine();
    Console.WriteLine("How much money do you wish to deposit? ");
    string Deposit = Console.ReadLine();
    float dBalance = float.Parse(Deposit);

    Console.WriteLine("Your new balance is " + (startBalance - dBalance) + " EUR");
    Console.ReadLine();
    Environment.Exit(0);
}
else 
{
    Console.WriteLine("There was no choice for this number");
}

【讨论】：

【解决方案2】：

复制+粘贴是邪恶的：请注意减法（加法预期）存款

"Your new balance is " + (startBalance - dBalance) + " EUR"

是典型复制+粘贴错误。

我们不要复制自己，而是提取一个方法：

private static float ReadFloat(string title) {
  // keep asking user...
  while (true) {
    if (!string.IsNullOrWhiteSpace(title))
      Console.WriteLine(title);

    if (!float.TryParse(Console.ReadLine(), out float result))
      Console.WriteLine("Syntax error. Please, try again.");
    else if (result < 0)
      Console.WriteLine("Negative sum is not allowed. Please, try again.");
    else
      return result; // ... until valid value is provided
  }
}

那就用吧

...

Console.WriteLine("Press 1 for WITHDRAWAL");
Console.WriteLine("Press 2 for DEPOSIT");

// Ask user once - Console.ReadKey().Key - then operate with his/her choice 
var choice = Console.ReadKey().Key;

// balance change (either negative - withdraw or positive - deposit)
float delta = 
    choice == ConsoleKey.NumPad1 ? -ReadFloat("How much money do you wish to withdraw?")
  : choice == ConsoleKey.NumPad2 ?  ReadFloat("How much money do you wish to deposit?")
  : 0f;

if (delta != 0) {
  Console.WriteLine($"Your new balance is {startBalance + delta} EUR");
  Console.ReadLine();
  Environment.Exit(0);
}
else 
  Console.WriteLine("There was no choice for this number");

【讨论】：