finished lab

index.js

@@ -4,7 +4,28 @@
  * 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() {
+    if (!process.argv[2]) {
+        return (`No operation provided...`)
+    } else if (!process.argv[3] || Number(process.argv[3] === "NaN")) {
+        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 result = 0;
+        for (let i = 3; i < process.argv.length; i++) {
+            result += Number(process.argv[i]);
+        } // end of loop
+        return result;
+    } else if (process.argv[2] === "minus") {
+        let product = (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;