Strings

Strings\n\nRust has two primary string types, each serving different purposes.\n\n## String vs &str\n\n### String\n- Owned, growable, heap-allocated text\n- Mutable by default (if declared mut)\n- Created with String::from() or .to_string()\n\n### &str\n- Borrowed string slice\n- Fixed size, immutable\n- String literals are &str\n\nrust\nlet s1: String = String::from(\"hello\"); // Owned\nlet s2: &str = \"world\"; // Borrowed (literal)\nlet s3: &str = &s1[..]; // Slice of String\n\n\n## Working with Strings\n\nrust\nfn main() {\n let mut s = String::from(\"Hello\");\n \n // Append string\n s.push_str(\", \");\n \n // Push single character\n s.push('W');\n \n // Concatenation with +\n let s2 = s + \"orld\"; // \"Hello, World\"\n \n // Format macro\n let s3 = format!(\"{}, {}\", s2, \"Rust\");\n}\n\n\n## String Operations\n\n### Length and Capacity\n\nrust\nlet s = String::from(\"hello\");\nprintln!(\"Length: {}\", s.len()); // 5 bytes\nprintln!(\"Capacity: {}\", s.capacity()); // Allocated space\n\n\n### Iteration\n\nrust\nlet s = \"hello\";\n\n// Bytes\nfor b in s.as_bytes() {\n println!(\"Byte: {}\", b);\n}\n\n// Characters (handles Unicode)\nfor c in s.chars() {\n println!(\"Char: {}\", c);\n}\n\n\n### Search and Replace\n\nrust\nlet s = \"hello world\";\nprintln!(\"Contains 'world': {}\", s.contains(\"world\")); // true\nprintln!(\"Starts with 'hello': {}\", s.starts_with(\"hello\")); //true\n\nlet replaced = s.replace(\"world\", \"Rust\");\nprintln!(\"Replaced: {}\", replaced); // \"hello Rust\"\n\n\n## Important: String Indexing\n\nYou cannot index strings with integers directly:\n\nrust\nlet s = String::from(\"hello\");\n// let c = s[0]; // ERROR!\n\n\nWhy? Strings are UTF-8 encoded, and characters can be multiple bytes. Use slicing or iteration instead:\n\nrust\nlet first_char = &s[0..1]; // Valid\n\n\n## Unicode Considerations\n\nrust\nlet s = \"hello\"; // Purely ASCII\nprintln!(\"Len: {}\", s.len()); // 5\n\nlet emoji = \"🦀\"; // 4 bytes\nprintln!(\"Len: {}\", emoji.len()); // 4 (bytes), not 1\nprintln!(\"Chars: {}\", emoji.chars().count()); // 1 (character)\n\n\n## String Conversion\n\nrust\nlet num = 42;\nlet s = num.to_string(); // \"42\"\n\nlet s2 = String::from(\"123\");\nlet num2: i32 = s2.parse().unwrap(); // 123\n\n\n## Best Practices\n\n1. Use &str for function parameters when possible\n2. Use String when you need to own the data\n3. Remember strings are UTF-8\n4. Use slicing, not indexing\n5. Use .to_string() for easy conversions