Add sheet 4

aufgaben/sheet4/task2/calculator.rs

@@ -0,0 +1,35 @@
+
+fn main() {
+    loop {
+        // Read input from the user and just do nothing when the input is empty
+        let input = read_string();
+        if input.is_empty() {
+            continue;
+        }
+
+        // Debug output
+        println!("{}", input);
+    }
+}
+
+
+/// Reads a string from the user (with a nice prompt).
+fn read_string() -> String {
+    use std::io::Write;
+
+    // Print prompt
+    print!("calc > ");
+    std::io::stdout().flush().unwrap();
+
+    // Read line
+    let mut buffer = String::new();
+    std::io::stdin()
+        .read_line(&mut buffer)
+        .expect("something went horribly wrong...");
+
+    // Discard trailing newline
+    let new_len = buffer.trim_right().len();
+    buffer.truncate(new_len);
+
+    buffer
+}