diff --git a/calc/main.swift b/calc/main.swift
index f3612d3..3646c90 100644
--- a/calc/main.swift
+++ b/calc/main.swift
@@ -11,4 +11,75 @@ import Foundation
 var args = ProcessInfo.processInfo.arguments
 args.removeFirst() // remove the name of the program
 
-print(Int(args[0])!)
+// command-line calculator
+
+// validation
+func validateArgs() {
+    for pos in 0...args.count-1 {
+        let operators = Set(["+", "-", "x", "/", "%"])
+        if (pos % 2 == 1 && !operators.contains(args[pos])) {
+            print("Invalid operator entered for argument \(pos+1).\nExiting with code 1...")
+            exit(1)
+        }
+        else if (pos % 2 == 0 && Int(args[pos]) == nil) {
+            print("Invalid integer entered for argument \(pos+1).\nExiting with code 1...")
+            exit(1)
+        }
+    }
+}
+
+// recursive x, / and % operands
+func recurseOperands(calc_data: [String], pos: Int) -> [String] {
+    var calc_data_mutable = calc_data
+    var increment = 2
+    
+    if pos > args.count - 1 {
+        return calc_data
+    }
+    else {
+        if (args[pos] == "x") {
+            let product = String(Int(calc_data.last!)! * Int(args[pos+1])!)
+            calc_data_mutable[calc_data_mutable.count-1] = product
+        }
+        else if (args[pos] == "/") {
+            if (Int(args[pos+1])! == 0) {
+                print("Error: Dividing by zero yields an undefined result.\nExiting with code 1...")
+                exit(1)
+            }
+            let dividend = String(Int(calc_data.last!)! / Int(args[pos+1])!)
+            calc_data_mutable[calc_data_mutable.count-1] = dividend
+        }
+        else if (args[pos] == "%") {
+            let remainder = String(Int(calc_data.last!)! % Int(args[pos+1])!)
+            calc_data_mutable[calc_data_mutable.count-1] = remainder
+        }
+        else {
+            calc_data_mutable.append(args[pos])
+            increment = 1
+        }
+    }
+    
+    return recurseOperands(calc_data: calc_data_mutable, pos: pos + increment)
+}
+
+validateArgs()
+
+var calc_data: [String] = recurseOperands(calc_data: [args[0]], pos: 1)
+var result: Int = Int(calc_data.first!)!
+
+for pos in 0...calc_data.count-1 {
+    if (pos < args.count) {
+        if (calc_data[pos] == "+") {
+            result += (Int(calc_data[pos+1])!)
+        }
+        else if (calc_data[pos] == "-") {
+            result -= (Int(calc_data[pos+1])!)
+        }
+    }
+    else {
+        print("Error: Calculation index is out of bounds.\nExiting with code 1...")
+        exit(1)
+    }
+}
+
+print(result)