Language: C++

// 参考
// https://techracho.bpsinc.jp/jhonda/2019_08_05/78537

// Input macro
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

macro_rules! stdin {
    () => {{
        use std::io::Read;
        let mut s = String::new();
        std::io::stdin().read_to_string(&mut s).unwrap();
        s
    }};
}

macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};

    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };

    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };

    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };

    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };

    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}

// Test Code
macro_rules! test {
    ($($input:expr => $output:expr),* $(,)*) => {
        #[test]
        fn solve_test() {
            $(
                assert_eq!(solve($input), $output);
            )*
        }
    };
}

test! {
r"21
" => r"27",

r"12
" => r"36"
}

use std::cmp;
use std::collections::HashSet;
use std::f32::MAX;

fn main() {
    println!("{}", solve(&stdin!()));
}

fn solve(src: &str) -> String {
    input! {
        source = src,
        m: i32
    }

    (48 - m).to_string()
}


Compiler output:
a.cc:47:10: error: too many decimal points in number
   47 |         (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
      |          ^~~~~~~
a.cc:66:10: error: invalid preprocessing directive #[
   66 |         #[test]
      |          ^
a.cc:76:2: warning: missing terminating " character
   76 | r"21
      |  ^
a.cc:76:2: error: missing terminating " character
   76 | r"21
      |  ^~~
a.cc:77:10: warning: missing terminating " character
   77 | " => r"27",
      |          ^
a.cc:77:10: error: missing terminating " character
   77 | " => r"27",
      |          ^~
a.cc:79:2: warning: missing terminating " character
   79 | r"12
      |  ^
a.cc:79:2: error: missing terminating " character
   79 | r"12
      |  ^~~
a.cc:80:10: warning: missing terminating " character
   80 | " => r"36"
      |          ^
a.cc:80:10: error: missing terminating " character
a.cc:5:1: error: 'macro_rules' does not name a type
    5 | macro_rules! input {
      | ^~~~~~~~~~~
a.cc:22:1: error: 'macro_rules' does not name a type
   22 | macro_rules! stdin {
      | ^~~~~~~~~~~
a.cc:31:1: error: 'macro_rules' does not name a type
   31 | macro_rules! input_inner {
      | ^~~~~~~~~~~
a.cc:41:1: error: 'macro_rules' does not name a type
   41 | macro_rules! read_value {
      | ^~~~~~~~~~~
a.cc:64:1: error: 'macro_rules' does not name a type
   64 | macro_rules! test {
      | ^~~~~~~~~~~
a.cc:75:1: error: 'test' does not name a type
   75 | test! {
      | ^~~~
a.cc:83:1: error: 'use' does not name a type
   83 | use std::cmp;
      | ^~~
a.cc:84:1: error: 'use' does not name a type
   84 | use std::collections::HashSet;
      | ^~~
a.cc:85:1: error: 'use' does not name a type
   85 | use std::f32::MAX;
      | ^~~
a.cc:87:1: error: 'fn' does not name a type
   87 | fn main() {
      | ^~
a.cc:91:1: error: 'fn' does not name a type
   91 | fn solve(src: &str) -> String {
      | ^~