diff --git a/index.js b/index.js
index 3bb4d07..d272b42 100644
--- a/index.js
+++ b/index.js
@@ -4,7 +4,35 @@
  * 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() {
+    let array = process.argv
+    let result = 0;
+    
+     if (array.length < 3){
+         return 'No operation provided...'
+     }
+     else if (!array[3]){
+         return 'No numbers provided...'
+     }
+     if (array[2] === 'plus') {
+         for (let i = 3; i < array.length; i++) {
+             result += Number(array[i]);
+         }
+         return result
+     }
+     else if (array[2] === 'minus'){
+         result = array[3]
+            for (let i = 4; i < array.length; i++){
+                result -= Number(array[i]);
+            }
+          return result
+     }
+    
+    else {
+        return `Invalid operation: ${array[2]}`;
+        }
+    }
+//for(let i = 0; i <= process.argv.length; i++) {  
 
 // 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": {