rust using regex in if statement

You can use the regex crate in Rust to match patterns using regular expressions in an if statement. Here's an example:

use regex::Regex;

fn main() {
    let re = Regex::new(r"^\d{4}$").unwrap();
    let input = "2023";

    if re.is_match(input) {
        println!("Input matches the regex pattern.");
    } else {
        println!("Input does not match the regex pattern.");
    }
}

In this example, we create a regular expression pattern that matches a string consisting of exactly four digits. We then use the is_match method of the Regex struct to check if the input matches the pattern. If it does, we print a message indicating a match; otherwise, we print a message indicating no match.

Remember to add the regex crate to your Cargo.toml file to use it in your Rust project.