diff --git a/index.js b/index.js
index 3bb4d07..ad3951f 100644
--- a/index.js
+++ b/index.js
@@ -1,10 +1,33 @@
+const { run } = require("jest");
+
 /**
  * The function below has no parameters. Instead, access the arguments from the command line.
  * The first argument passed after the filename should be either "plus" or "minus", which represents the kind of calculation that will be done. Every argument afterwards should be a number.
  * Depending on the operation, either add up all of the numbers or subtract all of the numbers, from left to right.
  * @returns {number} The result of either adding all numbers or subtracting all numbers, depending on the arguments added to the command line.
  */
-function calculator() {}
+function calculator() {
+    console.log(process.argv);
 
+    if ( !process.argv[2] ){
+        return `No operation provided...`
+    } else if ( !process.argv[3] ){
+        return 'No numbers provided...';
+    } else if ( process.argv[2] !== 'plus' && process.argv[2] !=='minus' ){
+        return `Invalid operation: ${process.argv[2]}`;
+    }else if ( process.argv[2] === 'plus' ){
+        let sum = 0
+        for(let i = 3; i < process.argv.length; i++){
+            sum += Number( process.argv[i])
+        }
+        return sum;
+    } else if ( process.argv[2] === 'minus'){
+        let product = Number( process.argv[3] )
+        for(let i = 4; i < process.argv.length;i++){
+            product -= Number( process.argv[i] )
+        }
+        return product;
+}
+}
 // Don't change anything below this line.
 module.exports = calculator;
diff --git a/package-lock.json b/package-lock.json
index 99b1c39..ce6f0ea 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -5,6 +5,7 @@
   "requires": true,
   "packages": {
     "": {
+      "name": "8-0-javascript-on-your-machine-lab",
       "version": "1.0.0",
       "license": "ISC",
       "devDependencies": {