Collections: Vec

Collections: Vec\n\nVec<T> (vector) is a growable array allocated on the heap. It's one of Rust's most-used collections.\n\n## Creating Vectors\n\nrust\nfn main() {\n // Empty vector\n let mut v: Vec<i32> = Vec::new();\n \n // Vec macro with initial values\n let v2 = vec![1, 2, 3];\n \n // Vec with repeated values\n let v3 = vec![5; 3]; // [5, 5, 5]\n}\n\n\n## Adding Elements\n\nrust\nfn main() {\n let mut v = Vec::new();\n v.push(1);\n v.push(2);\n v.push(3);\n println!(\"{:?}\", v); // [1, 2, 3]\n}\n\n\n## Reading Elements\n\nTwo ways to access elements with different behaviors:\n\nrust\nlet v = vec![1, 2, 3];\n\n// Using indexing (panics if out of bounds)\nprintln!(\"Element: {}\", v[0]); // 1\n// println!(\"Element: {}\", v[10]); // panics!\n\n// Using get (returns Option)\nmatch v.get(0) {\n Some(val) => println!(\"Element: {}\", val),\n None => println!(\"No element at index\"),\n}\n\n\n## Iterating Vectors\n\nrust\nlet v = vec![1, 2, 3];\n\n// Immutable iteration\nfor item in &v {\n println!(\"Item: {}\", item);\n}\n\n// Mutable iteration\nlet mut v = vec![1, 2, 3];\nfor item in &mut v {\n *item += 1; // Dereference to modify\n}\n\n// Consume vector\nlet v = vec![1, 2, 3];\nfor item in v {\n println!(\"Item: {}\", item); // v is consumed\n}\n// println!(\"{:?}\", v); // ERROR: v is moved\n\n\n## Useful Methods\n\nrust\nlet mut v = vec![1, 2, 3];\n\nprintln!(\"Length: {}\", v.len()); // 3\nprintln!(\"Capacity: {}\", v.capacity()); // At least 3\nprintln!(\"Is empty: {}\", v.is_empty()); // false\n\nlet last = v.pop(); // Some(3), v is now [1, 2]\nv.clear(); // Remove all elements\n\n\n## Working with Generic Vectors\n\nrust\nstruct User {\n name: String,\n age: u32,\n}\n\nfn main() {\n let mut users: Vec<User> = Vec::new();\n \n users.push(User {\n name: String::from(\"Alice\"),\n age: 30,\n });\n \n for user in &users {\n println!(\"{}: {}\", user.name, user.age);\n }\n}\n\n\n## Practical Example\n\nrust\nfn sum_vector(v: &Vec<i32>) -> i32 {\n let mut sum = 0;\n for &num in v {\n sum += num;\n }\n sum\n}\n\nfn double_all(v: &mut Vec<i32>) {\n for item in v {\n *item *= 2;\n }\n}\n\nfn main() {\n let mut numbers = vec![1, 2, 3, 4, 5];\n println!(\"Sum: {}\", sum_vector(&numbers)); // 15\n double_all(&mut numbers);\n println!(\"Doubled: {:?}\", numbers); // [2, 4, 6, 8, 10]\n}\n\n\n## Memory Efficiency\n\nVectors allocate in chunks (capacity > length):\n\n```rust\nlet mut v: Vec = Vec::new();\nprintln!("Capacity: {}", v.capacity()); // 0\n\nv.push(1);

println!("Capacity after push: {}", v.capacity()); // Usually 1\n\nfor i in 2..=10 {\n v.push(i);\n}\nprintln!("Final capacity: {}", v.capacity()); // Likely 16\n\n\nUse `reserve()` if you know approximate size:\n\nrust\nlet mut v = Vec::new();\nv.reserve(1000); // Allocate for 1000 elements\n```