diff --git a/src/chunk.zig b/src/chunk.zig
index db17a34..a3008c7 100644
--- a/src/chunk.zig
+++ b/src/chunk.zig
@@ -5,10 +5,14 @@ const Allocator = std.mem.Allocator;
 
 // hack. ugly hack. zig has compiler crash.
 const AllOpcodes = struct {
-    pub Constant: u8 = 0,
-    pub ConstantLong: u8 = 1,
-    pub Return: u8 = 2,
-    pub Negate: u8 = 3,
+    pub Return: u8 = 0,
+    pub Constant: u8 = 1,
+    pub ConstantLong: u8 = 2,
+    pub Add: u8 = 3,
+    pub Subtract: u8 = 4,
+    pub Multiply: u8 = 5,
+    pub Divide: u8 = 6,
+    pub Negate: u8 = 7,
 };
 
 pub const OpCode = AllOpcodes{};
@@ -151,6 +155,14 @@ pub const Chunk = struct {
             );
         } else if (instruction == OpCode.Negate) {
             return try simpleInstruction(stdout, "OP_NEGATE", index);
+        } else if (instruction == OpCode.Add) {
+            return try simpleInstruction(stdout, "OP_ADD", index);
+        } else if (instruction == OpCode.Subtract) {
+            return try simpleInstruction(stdout, "OP_SUBTRACT", index);
+        } else if (instruction == OpCode.Multiply) {
+            return try simpleInstruction(stdout, "OP_MULTIPLY", index);
+        } else if (instruction == OpCode.Divide) {
+            return try simpleInstruction(stdout, "OP_DIVIDE", index);
         } else {
             try stdout.print("Unknown opcode: {}\n", instruction);
             return index + 1;
diff --git a/src/main.zig b/src/main.zig
index d493e1a..8cd531f 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -116,8 +116,11 @@ pub fn main() !void {
     //var opcode_byte: u8 = @enumToInt(chunk.OpCode.Return);
     //try chk.write(chunk.OpCode.Return);
 
-    var constant = try chk.writeConstant(1.2, 123);
-    try chk.write(chunk.OpCode.Negate, 123);
+    try chk.writeConstant(1.2, 123);
+    try chk.writeConstant(3.4, 123);
+    try chk.write(chunk.OpCode.Add, 123);
+    try chk.writeConstant(5.6, 123);
+    try chk.write(chunk.OpCode.Divide, 123);
     try chk.write(chunk.OpCode.Return, 123);
 
     var vmach = vm.VM.init(stdout, &chk, true);
diff --git a/src/vm.zig b/src/vm.zig
index 5d74853..990f81f 100644
--- a/src/vm.zig
+++ b/src/vm.zig
@@ -81,6 +81,35 @@ pub const VM = struct {
         try self.stdout.print("\n");
     }
 
+    /// gets a f64 out of a value on the top of the stack.
+    fn popNum(self: *VM) f64 {
+        return self.pop();
+    }
+
+    fn doAdd(self: *VM) void {
+        var b = self.popNum();
+        var a = self.popNum();
+        self.push(a + b);
+    }
+
+    fn doSub(self: *VM) void {
+        var b = self.popNum();
+        var a = self.popNum();
+        self.push(a * b);
+    }
+
+    fn doMul(self: *VM) void {
+        var b = self.popNum();
+        var a = self.popNum();
+        self.push(a * b);
+    }
+
+    fn doDiv(self: *VM) void {
+        var b = self.popNum();
+        var a = self.popNum();
+        self.push(a / b);
+    }
+
     fn run(self: *VM) !InterpretResult {
         while (true) {
             if (self.debug_flag) {
@@ -108,6 +137,10 @@ pub const VM = struct {
                     return InterpretResult.Ok;
                 },
 
+                chunk.OpCode.Add => self.doAdd(),
+                chunk.OpCode.Subtract => self.doSub(),
+                chunk.OpCode.Multiply => self.doMul(),
+                chunk.OpCode.Divide => self.doDiv(),
                 chunk.OpCode.Negate => self.push(-self.pop()),
                 else => blk: {
                     std.debug.warn("Unknown instruction: {x}\n", instruction);