Added SimpleCalculator

src/test/java/com/thealgorithms/maths/Calculator/SimpleCalculator.java

@@ -0,0 +1,51 @@
+import java.util.Scanner;
+
+class public SimpleCalculator {
+    public static void main(String[] args) {
+        Scanner in = new Scanner(System.in);
+
+        System.out.println("""
+===== Simple Calculator =====
+1. Addition
+2. Subtraction
+3. Multiplication
+4. Division
+5. Exit
+Enter your choice: """);
+
+        int choice = in.nextInt();
+
+        switch (choice) {
+            case 1 : performOperation(in, '+');
+            case 2 : performOperation(in, '-');
+            case 3 : performOperation(in, '*');
+            case 4 : performOperation(in, '/');
+            case 5 : System.out.println("Exiting...");
+            default : System.out.println("Invalid choice! Please select between 1-5.");
+        }
+
+        in.close();
+    }
+
+    private static void performOperation(Scanner in, char operator) {
+        System.out.print("Enter 2 numbers: ");
+        int a = in.nextInt();
+        int b = in.nextInt();
+        int result = 0;
+
+        switch (operator) {
+            case '+' : result = a + b;
+            case '-' : result = a - b;
+            case '*' : result = a * b;
+            case '/' : {
+                if (b != 0) {
+                    result = a / b;
+                } else {
+                    System.out.println("Error: Division by zero!");
+                    return;
+                }
+            }
+        }
+        System.out.println("Result: " + result);
+    }
+}