Added program for calculator

Calculator.java

@@ -1,5 +1,44 @@
+import java.util.Scanner;
+
 public class Calculator{
   public static void main(String args[]){
-  System.out.println("Merge your modules here!");
-  }
+      System.out.println("Merge your modules here!");
+      Scanner sc = new Scanner(System.in);
+
+        System.out.println("Enter first number:");
+        double num1 = sc.nextDouble();
+
+        System.out.println("Enter second number:");
+        double num2 = sc.nextDouble();
+
+        System.out.println("Choose operation (+, -, *, /):");
+        char operator = sc.next().charAt(0);
+
+        double result;
+
+        switch (operator) {
+            case '+':
+                result = num1 + num2;
+                break;
+            case '-':
+                result = num1 - num2;
+                break;
+            case '*':
+                result = num1 * num2;
+                break;
+            case '/':
+                if (num2 != 0) {
+                    result = num1 / num2;
+                } else {
+                    System.out.println("Error: Division by zero!");
+                    return;
+                }
+                break;
+            default:
+                System.out.println("Invalid operator!");
+                return;
+        }
+
+        System.out.println("Result: " + result);
+    }
 }