What is the difference between StringBuilder and String in C#?

In C#, StringBuilder and String are both used for manipulating strings, but they have the following differences:

1. Mutability: StringBuilder is mutable, while String is immutable. This means that operations like modifying, inserting, or deleting can be performed on strings in a StringBuilder, whereas a String object cannot be changed. Modifying a String object will always create a new String object, which could potentially lead to performance issues.
2. Memory allocation: Because String is immutable, every operation on a String will create a new String object, resulting in frequent memory allocation. On the other hand, StringBuilder operates on an internal buffer when manipulating strings, only converting the buffer content into a String object when necessary, thus avoiding frequent memory allocation and improving performance.
3. Thread safety: StringBuilder is not thread-safe, meaning that concurrent operations on the same StringBuilder instance in a multi-threaded environment may lead to unpredictable results. On the other hand, String is thread-safe and can be shared between multiple threads without any issues.
4. Usage: StringBuilder is suitable for situations where frequent string modifications are needed due to its efficiency in string operations, such as string concatenation in loops or connecting a large number of strings. On the other hand, String is suitable for situations where string modifications are not frequent, such as string comparison or indexing.

In general, StringBuilder is suitable for scenarios where frequent string modifications are needed, as it can improve performance. On the other hand, String is suitable for scenarios where string modifications are not frequent, and it offers thread safety.