--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/calculate.cpp	Sun Oct 04 12:56:43 2026 -0500
@@ -0,0 +1,20 @@
+#include <stdexcept>
+#include "calculate.h"
+double calculate(double x, double y, char op) {
+  switch(op) {
+      default:
+        throw std::runtime_error("unknown sign");
+      case '*':
+        return x * y;
+      case '+':
+        return x + y;
+      case '-':
+        return x - y;
+      case '/':
+        if (y == 0) {
+          throw std::runtime_error("cannot divide by 0");
+        }
+        return x / y;
+    }
+}
+