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Declaring, Creating, and Initializing a String in C

Declaring a String Variable

To declare a string variable in C#, use the following syntax:

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string myString;
  • This tells the compiler that myString is a string variable.
  • At this point, myString is uninitialized and has a default value of null.

Note

  • A variable with a null value means it is not pointing to any object in memory. Trying to use myString without assigning a value will result in a runtime error.

Understanding Reference Types

Strings, like arrays, are reference types. This means:

  • Stack vs. Heap Memory:
    • The variable myString on the stack holds a reference (memory address) to the actual string object stored on the heap.
    • When you declare a string without assigning a value, the variable exists but does not reference any object in memory.

Instantiating and Initializing a String

Before using a string, you must initialize it by assigning a value:

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myString = "Hello, World!";
string name = "";
  • The string literal "Hello, World!" is created in the heap, and myString holds a reference to this location.
  • name is initialized as an empty string ("").

Warning

  • Declaring a string variable without assigning a value and then trying to use it will result in a NullReferenceException.

Copying String References

If you assign one string variable to another, you're copying the reference, not the value:

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string myNewString = myString;
  • This means myNewString now points to the same memory location as myString.
  • Any changes to the string object will be reflected in both variables.

Note

  • Even though strings are reference types, they are immutable. This means you cannot change the value of an existing string object in memory. Any modification results in a new string object being created.

String Initialization in One Step

You can declare and initialize a string in a single step:

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string greeting = "Welcome to A Level Computer Science!";

Reading and Printing Strings

We have seen these methods quite a bit in previous sections, but copied here for completeness.

Reading from the Console

The ReadLine() method reads a line of text entered by the user and returns it as a string:

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Console.Write("Enter your name: ");
string name = Console.ReadLine();
  • The ReadLine() method waits for the user to press Enter and assigns the input to the name variable.

Printing to the Console

The WriteLine() method prints a string to the console:

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Console.WriteLine("Hello, " + name + "!");
  • This uses string concatenation to combine the greeting and the name variable.

String Interpolation

String interpolation provides a more readable way to include variables in strings:

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Console.WriteLine($"Hello, {name}!");
  • The $ symbol before the string allows you to embed variables directly within the curly braces {}.

Advantages of String Interpolation: - More readable and easier to manage, especially with complex strings. - Avoids the need to use the + operator for concatenation.