Rust println! result is different that print! when using time::sleep

Ok, so I haven't worked with Rust for that long so sorry if this is dumb. But I'm trying to make a print function that takes in a string and then prints the string character by character on the same line and has a pause between each character. Here's the function:

fn talk(input: String){
    let inputVec: Vec<char> = input.chars().collect();
    
    let mut i = 0;
    loop{
        thread::sleep(time::Duration::from_millis(100));
        if i >= inputVec.len() {
            break;
        }
        print!("{}", inputVec[i]);
        i = i + 1;
    }
}

When I do this code with the print! macro, it doesn't work and just waits 100 milliseconds before printing the string as one print! call. But if I use println! then it works perfectly minus the new line for every character. Can someone help me with this or at least tell me why it doesn't work?

Like the comments of Vivick and drewtato, you need use flush of Write io's module Trait.

use std::{thread, time};
use std::io::{self, Write};

fn main() {
    talk("Hello, world!\n".to_string());
}

fn talk (input: String) {
    let chars = Vec::<u8>::from(input);
    let mut i = 0;
    while i < chars.len() {
        print!("{}", chars[i] as char);
        io::stdout().flush().unwrap();
        thread::sleep(time::Duration::from_millis(100));
        i+=1;
    }
}

This works for me!

But, the most simple way to do this is use eprint! macro, like this:

use std::{thread, time};

fn main() {
    talk("Hello, world!\n".to_string());
}

fn talk (input: String) {
    let chars = Vec::<u8>::from(input);
    let mut i = 0;
    while i < chars.len() {
        eprint!("{}", chars[i] as char);
        thread::sleep(time::Duration::from_millis(100));
        i+=1;
    }
}

and the documentation says:

Use eprint! only for error and progress messages. Use print! instead for the primary output of your program.