fix: under/overflow

src/main.rs

@@ -11,8 +11,8 @@ fn interpret(code: &str) {
         match code_bytes[pc] as char {
             '>' => head += 1,
             '<' => head -= 1,
-            '+' => memory[head] += 1,
+            '+' => memory[head] = memory[head].wrapping_add(1),
-            '-' => memory[head] -= 1,
+            '-' => memory[head] = memory[head].wrapping_sub(1),
             '.' => println!("{}", memory[head]),
             ',' => {
                 let mut input_buf = [0u8; 1];