Rust HashMap Key-Value Update & Printing

Rust Arrays: Exercise-5 with Solution

Write a Rust program to update the value associated with a key in a HashMap and print the updated HashMap.

Sample Solution:

Rust Code:

use std::collections::HashMap; // Import the HashMap type from the standard library

fn main() {
    // Create a HashMap to store key-value pairs
    let mut my_map: HashMap<&str, i32> = HashMap::new(); // Key: &str (string slice), Value: i32

    // Insert some key-value pairs into the HashMap
    my_map.insert("a", 1);
    my_map.insert("b", 2);
    my_map.insert("c", 3);

    // Print the original HashMap
    println!("Original HashMap: {:?}", my_map);

    // Define the key for which to update the value
    let key_to_update = "b";
    let new_value = 42; // New value to assign to the key

    // Update the value associated with the key in the HashMap
    match my_map.get_mut(key_to_update) {
        Some(value) => *value = new_value, // If the key exists, update the value
        None => println!("Key '{}' does not exist in the HashMap.", key_to_update), // If the key does not exist, print a message
    }

    // Print the updated HashMap
    println!("Updated HashMap: {:?}", my_map);
}

Output:

Original HashMap: {"c": 3, "b": 2, "a": 1}
Updated HashMap: {"c": 3, "b": 42, "a": 1}

Explanation:

Here is a brief explanation of the above Rust code:

• use std::collections::HashMap;: This line imports the "HashMap" type from the standard library, allowing us to use HashMaps in our code.
• fn main() { ... }: This line defines the main function, which is the entry point of the Rust program.
• let mut my_map: HashMap<&str, i32> = HashMap::new();: This line creates an empty HashMap named 'my_map' with keys of type &str (string slice) and values of type i32.
• my_map.insert("a", 1);: This line inserts a key-value pair into the 'my_map' HashMap, where the key is the string slice "a" and the value is the integer 1. Similar lines insert additional key-value pairs.
• println!("Original HashMap: {:?}", my_map);: This line prints the original HashMap before any updates are made.
• let key_to_update = "b";: This line defines the key for which we want to update the associated value in the HashMap.
• let new_value = 42;: This line defines the new value that we want to assign to the key in the HashMap.
• match my_map.get_mut(key_to_update) { ... }: This line attempts to retrieve a mutable reference to the value associated with the specified key from the HashMap using the "get_mut()" method. The "match" statement is used to handle the result:
• If the key exists (Some(value)), it updates the value associated with the key to the new value (*value = new_value).
• If the key does not exist (None), it prints a message indicating that the key does not exist in the HashMap.
• println!("Updated HashMap: {:?}", my_map);: This line prints the updated HashMap after the value associated with the specified key has been updated.

Rust Code Editor:

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