symb_diff.rs

symb_diff.rs

use std::io::{stdin,stdout,Write};
use regex::Regex;
/* Polynomial: involves only the operations 
 * of addition, subtraction, multiplication, 
 * and non-negative integer exponentiation 
 * of variables
*/

fn main() {
    //get user input
    let mut s = String::new();
    print!("Equation: ");
    let _=stdout().flush();
    stdin().read_line(&mut s).expect("Did not enter a correct string");
    
    //validate input
    let re = Regex::new(r"^(\d?[a-z]\^\d(\+|\-)?|[a-z](\+|\-)?|\d(\+|\-)?)+\r?\n$").unwrap();
    assert!(re.is_match(&s));
    
    let mut tmp: u32 = 0; //used for storing intermediate values in chars -> integer
    let mut prev: u32 = 0; //used to store the multiplicand, if applicable
    let mut x_flag = false; //checking if x has been encountered in the block

    let mut eq = String::new();

    for c in s.chars() {
        match c {
            '0'..='9' => {
                tmp = tmp * 10 + (c as u8 - b'0') as u32; //char to integer
            },
            '^' => {
                //^ -> will encounter a second digit (the exponent) 
                prev = tmp;
                tmp = 0
            },
            'x' => x_flag = true,
            '-' | '+' | '\n' => {
                if x_flag {
                    if prev == 0 { //no exponent, as prev has not been assigned to tmp upon '^'
                        eq.push_str(&format!(" {} {}", tmp, c)); //ie 8x+ -> 8 +
                    }
                    else {
                        if tmp == 2 { 
                            eq.push_str(&format!(" {}x {}", prev*tmp, c)); //3x^2 -> 6x [as opposed to 6x^1]
                        } else {
                            eq.push_str(&format!(" {}x^{} {}", prev*tmp, tmp-1, c));
                        }
                    }
                }
                tmp = 0;
                prev = 0;
                x_flag = false;
            },
            _ => ()
        }
    }

    println!("d/dx = {}", eq.trim());
}

Cargo.toml

[package]
name = "sdiff"
version = "0.1.0"
edition = "2021"

[dependencies]
regex="1"