在 C# 字典中使用 ToUpper 和 ToLower 来检查 ContainsKey 的用户输入

Question

Trying to use ToUpper and ToLower validation in a C# Console Application to verify if a user defined string is inside a Dictionary with string and int elements inside it, printing out the elements with ConstainsKey afterward. For example (simplified):

Dictionary<string, int> example = new Dictionary<string, int>();

//int for number of each type of element
int elements = 3;

for (int i = 0; i < elements; i++)
{
     Console.WriteLine("What is the key?");
     string stringElement = Console.ReadLine();
     
     //Validation loop
     while (string.IsNullOrWhileSpace(stringElement))
     {
          Console.WriteLine("error");
          Console.WriteLine("What is the key?");
          stringElement = Console.ReadLine();
     }
     //Ask user for value
     Console.WriteLine("What is the value?");

     string numElementString = Console.ReadLine();

     while (string.IsNullOrWhiteSpace(intElementString) || (!(int.TryParse(numElementString, out numElement))) || numElement <= 0)
     {
          Console.WriteLine("error");
          Console.WriteLine("What is the value?");
          numElementString = Console.ReadLine();
     }
     example.Add(stringElement, numElement);
}

//What does user want to have printed
Console.WriteLine("What elements are you looking for? Please type in the key you need.");

//Catch key user answers
string userAnswer = Console.ReadLine();

//userAnswer validation look for IsNullOrWhiteSpace
while (string.IsNullOrWhiteSpace(userAnswer))
{
     Console.WriteLine("error");
     Console.WriteLine("What elements are you looking for? Please type in the key you need.");
     userAnswer = Console.ReadLine();

I got that far, I'm just having an issue with using the ToUpper and ToLower expressions to have the console print out the specific <string, int> variables that are inside the dictionary the user wants from the specified user input. Any push in the right direction will help... just want a simple solution for now since I'm still getting into the programming language.

Answer 1

You don't need to use ToUpper or ToLower to try to find a key in a case-insensitive way. Instead, you can pass a comparer to the constructor of the dictionary that specifies that it should ignore case when adding or retrieving items:

var dict = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);

Now, when you search for a value, it will do a case-insensitive comparison to try to find it:

// Add a value using lower case key
dict.Add("foo", "bar");  

// Search for a value using upper case returns 'true'
if (dict.ContainsKey("FOO")) { } 

And trying to add a key with a different case will throw an ArgumentException with the message "An item with the same key has already been added."

dict.Add("Foo", "bar2")  // Argument exception - key already exists