Add support for math operations

inp.txt

@@ -1 +1,3 @@
-pHello pWorld!
+pHello pWorld! 
+a15-16 s19-4 m3-3 d9-3
+

src/eval.rs

@@ -0,0 +1,21 @@
+pub fn do_math(arguments: &str, operator: char) -> u32 {
+    let split_args = arguments.split("-").collect::<Vec<&str>>();
+
+    let num1: u32 = match split_args[0].parse() {
+        Ok(num) => num,
+        Err(_e) => panic!("ArgumentError: Not a number: {}", split_args[0])
+    };
+
+    let num2: u32 = match split_args[1].parse() {
+        Ok(num) => num,
+        Err(_e) => panic!("ArgumentError: Not a number: {}", split_args[1])
+    };
+    
+    match operator {
+        '+' => num1 + num2,
+        '-' => num1 - num2,
+        '*' => num1 * num2,
+        '/' => num1 / num2,
+        _ => panic!("SyntaxError: Unknown operator {}", operator)
+    }
+}

src/main.rs

@@ -3,6 +3,8 @@ use std::env;
 use std::fmt;
 use std::usize;
 
+mod eval;
+
 struct Program {
     data: Vec<String>,
     pc: usize
@@ -24,12 +26,15 @@ impl Program {
     }
 
     fn eval(&self, instruction: &String) {
-        let instruction_vec: Vec<char> = instruction.chars().collect();
-        let opcode = instruction_vec[0];
+        let opcode = instruction.chars().collect::<Vec<char>>()[0];
         let arguments = &instruction[1..];
 
         match opcode {
             'p' => println!("{}", arguments),
+            'a' => println!("{}", eval::do_math(arguments, '+')),
+            's' => println!("{}", eval::do_math(arguments, '-')),
+            'm' => println!("{}", eval::do_math(arguments, '*')),
+            'd' => println!("{}", eval::do_math(arguments, '/')),
             _ => panic!("SyntaxError at opcode {}!", self.pc)
         }
     }