import java.util.Scanner; // importing the scanner from java.util

class simplecalculator{ // Creating a class

public static void main(String[] args) {

Scanner userinput = new Scanner(System.in); // Creating an object for userinput.

while(true){ // Infinite loop to allow multiple calculations until user exits.

// displaying the calculator header

System.out.println(" \n -------------------");

System.out.println(" | Simple Calculator |");

System.out.println(" -------------------");

// Displaying the available operations

System.out.println("\nselect your choice of operation from the below options (1 - 4)numbers only:");

System.out.println("----------------------------------------------------------------------------");

System.out.println("1.)Addition\n2.)substraction\n3.)multplication\n4.)division");

System.out.println("enter your choice from (1- 4) : ");

// looking for the invalid input for choice ( Ensuring that the user can only select the numeric only values)

if(!userinput.hasNextInt()){

System.out.println(" Invalid Input : you cannot select non - numeric values ");

System.out.println("\nselect your choice of operation from the options (1 - 4)numbers only:");

userinput.next();

continue; // Restart the loop again.

}

// Exit the loop here by seledcting number "0"

int choice = userinput.nextInt();

if(choice == 0){

System.out.println(" Thankyou for using simple calculator. !!! GOODBYE !!!");

break;

}

// checking for the invalidation of choice.

if (choice >4) {

System.out.println("Invalid choice! Please select a valid option.");

continue; // Restart the loop again.

}

// Reading the first number

System.out.println("Enter your first number:");

if (!userinput.hasNextDouble()) { // Checking if input is a valid number

System.out.println("Invalid input! Please enter a valid number.");

userinput.next(); // Clear invalid input

continue; // Restart the loop

}

double num1 = userinput.nextDouble(); // Reading first number

// Reading the second number

System.out.println("Enter your Second number:");

if (!userinput.hasNextDouble()) { // Checking if input is a valid number

System.out.println("Invalid input! Please enter a valid number.");

userinput.next(); // Clear invalid input

continue; // Restart the loop

}

double num2 = userinput.nextDouble(); // Reading Second number

double result;

// Performing the selected operation

if(choice==1){ // ADDITION

result = num1+num2;

System.out.println("The addition of "+num1+" + "+num2+" = "+result);

}

else if(choice==2){ //SUBSTRACTION

result = num1-num2;

System.out.println("The Substraction of "+num1+" + "+num2+" = "+result);

}

else if(choice==3){ //MULTIPLICATION

result = num1*num2;

System.out.println("The Multiply of "+num1+" + "+num2+" = "+result);

}

else if(choice==4){ // DIVISION

if(num1==0 || num2==0){ // Checking the num1 and num2 for input "0". Because the division is not possible with zero.

System.out.println("Error : Division by zero is not allowed.");

}

else{

result = num1/num2;

System.out.println("The Division of "+num1+" + "+num2+" = "+result);

}

}

}

userinput.close(); // Closing the Scanner to prevent resource leaks

}

}