What is the difference between StringBuilder and string concatenation?

Question

Accepted Answer

**StringBuilder** — mutable. **string** — immutable.

**StringBuilder:**
- Mutable.
- Efficient.
- Multiple operations.

**string:**
- Immutable.
- Allocates.
- Simple.

```csharp
// StringBuilder
var sb = new StringBuilder();
for (int i = 0; i < 100; i++)
    sb.AppendLine($"Line {i}");
var result = sb.ToString();

// string concatenation
var result = "";
for (int i = 0; i < 100; i++)
    result += $"Line {i}
";  // Slow
```

**Key:** StringBuilder for loops, string for simple.

C#: What is the difference between StringBuilder and string concatenation?