如何在 C# 控制台中使用用户输入添加堆栈推送

Question

Im stuck on adding a push when a user inputs a data. The program functions this way like, when I enter a key like the letter A, it will add to the stack and show that the stack has 1 entity. But im stuck, it should be when I enter another key it will add to the stack. Here is my code.

while (true)
        {
            string letter = null;
            Console.WriteLine("Enter A = Apple, O = Orange, M = Mango, G = Guava");
            letter = Console.ReadLine();
            

            if (letter == "a")
            {
                Stack<string> myStack = new Stack<string>();
                myStack.Push(letter);
                Console.WriteLine("Fruits in the basket x " + myStack.Count);
                
               if(letter == "o") {
                    myStack.Push(letter);
                    Console.WriteLine("Fruits in the basket x " + myStack.Count);
                }

any suggestions and help will be greatly appreciated! Thankyou in advance!

Answer 1

There are quite a few things wrong here. Let's list them

1. Nested if s.
   Your if(letter == "o") is nested inside the check if (letter = "a") which means it will always be false

2. Console.ReadLine() returns after pressing Enter , not after pressing any key
   Console.ReadLine() doesn't return each individual key press after they happened, it returns the entire sequence of characters (aka a string) pressed only after you pressed Enter

3. Declaring your Stack inside the if statement for a
   What if I want to add an orange as my first item? This would throw an exception (if you fix your nested if issue) as it won't be defined when trying to access it. It will also re-create the stack every time an apple is added, meaning, the stack will be cleared out and you'll never be able to have more than 1 Apple inside your stack.

4. Repeated code
   Inside all your if statements is the exact same code, so there's no need for multiple statements, only one checking if the letter is any we accept

Here's how to fix them:

// Declare myStack once, so it doesn't get reset every time we add an Apple
Stack<char> myStack = new Stack<char>();

while (true)
{
    Console.WriteLine("A = Apple, O = Orange, M = Mango, G = Guava");
    
    // Use Console.ReadKey not ReadLine to capture each key press separately
    // The 'true' parameter prevents the console from showing what character we pressed
    ConsoleKeyInfo keyPressed = Console.ReadKey(true);
    char characterPressed = keyPressed.KeyChar;
    
    if (characterPressed == 'a' || characterPressed == 'o' || characterPressed == 'm' || characterPressed == 'g')
    {
        myStack.Push(characterPressed);
    }
    else
    {
        Console.WriteLine("You pressed a non-valid character");
    }
    
    Console.WriteLine("Fruits in the basked x " + myStack.Count);
}

Answer 2

After you go into the if (letter == "a") statement you never reassign letter. So when it gets to if(letter == "o") letter still equals "a".

Above the second if statement you need to add letter = Console.ReadLine(); as below:

letter = Console.ReadLine();
if(letter == "o")