我正在自学 C#，当前的章节挑战要求我：
以您的最后一个项目并创建附加的方法，将传递给它的两个数字相减、相乘或相除。在除法中，检查第二个数是否不为 0，因为除以 0 是一个非法的数学概念。如果第二个数字是 0，则返回 0。
现在我写了以下我认为满足所有标准的内容。我不确定 IF 语句是否是最佳选择，但它确实有效。我还认为 SWITCH 也可以解决问题。
所以第一个问题，IF 或 SWITCH 会更好吗？
第二个问题。在 ELSE 中，如果用户没有选择可用选项之一，我会给出一般失败消息，但我想做的是如果调用 ELSE（不确定正确的术语是什么），我希望程序回到开始并要求用户再试一次并显示第一个 Console.Writeline() 要求选择操作员。我知道这不是挑战的一部分，但它似乎是对程序的合乎逻辑的补充，我想知道这是否可行，而无需诉诸任何过于复杂的东西。
提前致谢！
string whichOp;
int firstNum, secondNum, result;
Console.WriteLine("What Operator do you wish to use? [A]dd, [S]ubtract, [M]ultiply or [D]ivide?");
whichOp = Console.ReadLine();
whichOp = whichOp.ToLower();
if (whichOp == "a")
{
Console.Write("You chose Addition. Please choose your first number: ");
firstNum = int.Parse(Console.ReadLine());
Console.Write("You chose the number {0}. Please choose a second number: ", firstNum);
secondNum = int.Parse(Console.ReadLine());
result = Add(firstNum, secondNum);
Console.WriteLine("You chose the number {0}. {1} plus {2} equals {3}.", secondNum, firstNum, secondNum, result);
}
else if (whichOp == "s")
{
Console.Write("You chose Subtraction. Please choose your first number: ");
firstNum = int.Parse(Console.ReadLine());
Console.Write("You chose the number {0}. Please choose a second number: ", firstNum);
secondNum = int.Parse(Console.ReadLine());
result = Sub(firstNum, secondNum);
Console.WriteLine("You chose the number {0}. {1} minus {2} equals {3}.", secondNum, firstNum, secondNum, result);
}
else if (whichOp == "m")
{
Console.Write("You chose Multiplication. Please choose your first number: ");
firstNum = int.Parse(Console.ReadLine());
Console.Write("You chose the number {0}. Please choose a second number: ", firstNum);
secondNum = int.Parse(Console.ReadLine());
result = Mult(firstNum, secondNum);
Console.WriteLine("You chose the number {0}. {1} times {2} equals {3}.", secondNum, firstNum, secondNum, result);
}
else if (whichOp == "d")
{
Console.Write("You chose Division. Please choose your first number: ");
firstNum = int.Parse(Console.ReadLine());
Console.Write("You chose the number {0}. Please choose a second number: ", firstNum);
secondNum = int.Parse(Console.ReadLine());
result = Div(firstNum, secondNum);
Console.WriteLine("You chose the number {0}. {1} divided by {2} equals {3}.", secondNum, firstNum, secondNum, result);
}
else
Console.WriteLine("FAIL! You did not choose an available option.");
Console.ReadLine();
}
static int Add(int num1, int num2)
{
int theAnswer;
theAnswer = num1 + num2;
return theAnswer;
}
static int Mult(int num1, int num2)
{
int theAnswer;
theAnswer = num1 * num2;
return theAnswer;
}
static int Sub(int num1, int num2)
{
int theAnswer;
theAnswer = num1 - num2;
return theAnswer;
}
static int Div(int num1, int num2)
{
int theAnswer;
if (num2 == 0)
return 0;
theAnswer = num1 / num2;
return theAnswer;
}
编辑：我接受了这里的建议，并用 SWITCH 和 WHILE 重建了程序。也有人说，因为很多代码都是一样的，我应该可以重用它。我喜欢这个想法，并将研究如何做到这一点。
var retry = true;
while (retry)
{
retry = false;
string whichOp;
int firstNum, secondNum, result;
Console.WriteLine("What Operator do you wish to use? [A]dd, [S]ubtract, [M]ultiply or [D]ivide?");
whichOp = Console.ReadLine();
whichOp = whichOp.ToLower();
switch (whichOp)
{
case "a":
Console.Write("You chose Addition. Please choose your first number: ");
firstNum = int.Parse(Console.ReadLine());
Console.Write("You chose the number {0}. Please choose a second number: ", firstNum);
secondNum = int.Parse(Console.ReadLine());
result = Add(firstNum, secondNum);
Console.WriteLine("You chose the number {0}. {1} plus {2} equals {3}.", secondNum, firstNum, secondNum, result);
Console.ReadLine();
break;
case "s":
Console.Write("You chose Subtraction. Please choose your first number: ");
firstNum = int.Parse(Console.ReadLine());
Console.Write("You chose the number {0}. Please choose a second number: ", firstNum);
secondNum = int.Parse(Console.ReadLine());
result = Sub(firstNum, secondNum);
Console.WriteLine("You chose the number {0}. {1} minus {2} equals {3}.", secondNum, firstNum, secondNum, result);
Console.ReadLine();
break;
case "m":
Console.Write("You chose Multiplication. Please choose your first number: ");
firstNum = int.Parse(Console.ReadLine());
Console.Write("You chose the number {0}. Please choose a second number: ", firstNum);
secondNum = int.Parse(Console.ReadLine());
result = Mult(firstNum, secondNum);
Console.WriteLine("You chose the number {0}. {1} times {2} equals {3}.", secondNum, firstNum, secondNum, result);
Console.ReadLine();
break;
case "d":
Console.Write("You chose Division. Please choose your first number: ");
firstNum = int.Parse(Console.ReadLine());
Console.Write("You chose the number {0}. Please choose a second number: ", firstNum);
secondNum = int.Parse(Console.ReadLine());
result = Div(firstNum, secondNum);
Console.WriteLine("You chose the number {0}. {1} divided by {2} equals {3}.", secondNum, firstNum, secondNum, result);
Console.ReadLine();
break;
default:
Console.WriteLine("I'm sorry. {0} is not an available option. Please try again.", whichOp.ToUpper());
retry = true;
break;
}
}
}
static int Add(int num1, int num2)
{
int theAnswer;
theAnswer = num1 + num2;
return theAnswer;
}
static int Mult(int num1, int num2)
{
int theAnswer;
theAnswer = num1 * num2;
return theAnswer;
}
static int Sub(int num1, int num2)
{
int theAnswer;
theAnswer = num1 - num2;
return theAnswer;
}
static int Div(int num1, int num2)
{
int theAnswer;
if (num2 == 0)
return 0;
theAnswer = num1 / num2;
return theAnswer;
}