Round #873

Use a Span<char> to parse an integer from a string slice without allocating. Compare to int.Parse(string) qualitatively.

```csharp using System; class Program { static int ParseInt(string s) { int result = 0; foreach (char c in s) { if (char.IsDigit(c)) { result = result * 10 + (c - '0'); } else { throw new FormatException("Input string contains non-numeric characters"); } } return result; } static void Main() { string s = "12345"; Console.WriteLine(ParseInt(s)); // Output: 12345 } } ```

```csharp using System; public class IntegerParser { public static bool TryParseInteger(Span<char> input, out int result) { result = 0; int sign = 1; int index = 0; // Check for negative sign if (input.Length > 0 && input[0] == '-') { sign = -1; index++; } // Check for positive sign else if (input.Length > 0 && input[0] == '+') { index++; } for (; index < input.Length; index++) { if (input[index] >= '0' && input[index] <= '9') { // Check for overflow if (result > (int.MaxValue - (input[index] - '0')) / 10) { return false; } result = result * 10 + (input[index] - '0'); } else { return false; } } result *= sign; return true; } public static void Main() { var input = "123".AsSpan(); if (TryParseInteger(input, out int result)) { Console.WriteLine($"Parsed integer: {result}"); } else { Console.WriteLine("Failed to parse integer"); } } } ``` The `TryParseInteger` method using `Span<char>` avoids allocating memory by operating directly on the input string slice. In contrast, `int.Parse(string)` allocates memory for the string object and may throw exceptions for invalid input. The `Span<char>` approach is more efficient and safer, as it returns a boolean indicating success or failure instead of throwing exceptions. However, `int.Parse(string)` is often more convenient and easier to use, especially for simple cases. The choice between the two approaches depends on the specific requirements of the application, such as performance, memory usage, and error handling. This implementation requires more code and manual error checking, but provides more control and flexibility.