Java If a user inputs a character, I want it to go back to the beginning and say "Please input a number".

[Jarrett.mueller]

package Term1.part1;

import java.util.Scanner;

public class Calculator_2 {
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
System.out.println("Welcome to Jarrett's Shitty Calculator");

boolean doMath = true;
boolean firstTime = true;
int result = 0;

String operations = "";

do {
System.out.println("Answer = " + result + "\n1 - Addition\n2 - Subtraction\n3 - Multiplication\n4 - Division\n5 - Quit");
int choice = keyboard.nextInt();

if (choice < 1 || choice > 5) {
System.out.println("Incorrect input, please select a number between 1 & 5.");
result = 0;
} else if (choice == 5) {
System.out.println("Closing Application.");
doMath = false;
} else if (choice == ) {

}

} else {
int a;

if (firstTime) {
System.out.print("Enter the first number: ");
a = keyboard.nextInt();
} else {
a = result;
}

operations += String.valueOf(a);

System.out.print("Enter the second number: ");
int b = keyboard.nextInt();

switch (choice) {
case 1:
result = a + b;
operations += " + ";
break;
case 2:
result = a - b;
operations += " - ";
break;
case 3:
result = a * b;
operations += " * ";
break;
case 4:
result = a / b;
operations += " / ";
break;
default:
System.out.println("Incorrect sequence of operations.");

}
operations += String.valueOf(b) + " = " + result + "\n";
}
}
while (doMath);
System.out.println(operations);
}
}

 

[EkBass]

Please edit your post and place the code inside of code tags. It is terrible to read it now.

 

[ratwolf]

Please edit your post and place the code inside of code tags. It is terrible to read it now.

Fully agree

 

[Jarrett.mueller]

I apologize about that. I am not the best with this. I will do that now.

 

[Jarrett.mueller]

package Term1.part1;

import java.util.Scanner;

public class Calculator_2 {
    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.println("Welcome to Jarrett's Shitty Calculator");

        boolean doMath = true;
        boolean firstTime = true;
        int result = 0;

        String operations = "";

        do {
            System.out.println("Answer = " + result + "\n1 - Addition\n2 - Subtraction\n3 - Multiplication\n4 - Division\n5 - Quit");
            int choice = keyboard.nextInt();

            if (choice < 1 || choice > 5) {
                System.out.println("Incorrect input, please select a number between 1 & 5.");
                result = 0;
            } else if (choice == 5) {
                System.out.println("Closing Application.");
                doMath = false;
            } else if (choice == ) {
                
            }

        } else {
                    int a;

                    if (firstTime) {
                        System.out.print("Enter the first number: ");
                        a = keyboard.nextInt();
                    } else {
                        a = result;
                    }

                    operations += String.valueOf(a);

                    System.out.print("Enter the second number: ");
                    int b = keyboard.nextInt();

                    switch (choice) {
                        case 1:
                            result = a + b;
                            operations += " + ";
                            break;
                        case 2:
                            result = a - b;
                            operations += " - ";
                            break;
                        case 3:
                            result = a * b;
                            operations += " * ";
                            break;
                        case 4:
                            result = a / b;
                            operations += " / ";
                            break;
                        default:
                            System.out.println("Incorrect sequence of operations.");

                    }
                    operations += String.valueOf(b) + " = " + result + "\n";
                }
            }
            while (doMath);
            System.out.println(operations);
        }
    }

 

[EkBass]

Here is actually pretty nifty tutorial how to check is input a valid number.

Check If a String Is Numeric in Java | Baeldung

Explore different ways to determine whether a String is numeric or not.

www.baeldung.com

 

[Jarrett.mueller]

Here is actually pretty nifty tutorial how to check is input a valid number.

Check If a String Is Numeric in Java | Baeldung

Explore different ways to determine whether a String is numeric or not.

www.baeldung.com

Thank you! I'll take a look.