Search code examples
javaif-statementuser-input

My program doesn't find the variable inside the if statement even when I've defined it outside the if statement(simple calculator)

I added a if statement that parses a entered number into a double to use when I do my calculations in the second if statement block, the program has to run if only numbers where entered and not letters, the program doesn't seem to read the numbers when I entered a double(5.5) but works fine when I enter a int(5) number/numbers.

Scanner numbers = new Scanner(System.in);
Scanner operation = new Scanner(System.in);

double number1 = 0;
double number2 = 0;
String operator;


System.out.print("Enter the operator you would like to choose(+, -, *, /): ");
operator = operation.next();


System.out.print("Enter the first number: ");
String num1 = numbers.nextLine();


System.out.print("Enter your second number: ");
String num2 = numbers.nextLine();


boolean check1 = num1.trim().matches("^[0-9]+$");
boolean check2 = num2.trim().matches("^[0-9]+$");


if (check1 == true && check2 == true){
    number1 = Double.parseDouble(num1);
    number2 = Double.parseDouble(num2);
}else {
    System.out.println("Only enter numbers not letters.");
}


String calculation;
if (operator.equals("+")){
    calculation = (number1 + " + " + number2 + " = " + (number1 + number2));
    System.out.println(calculation);

}else if (operator.equals("-")){
    calculation = (number1 + " - " + number2 + " = " + (number1 - number2));
    System.out.println(calculation);

}else if (operator.equals("*")){
    calculation = (number1 + " * " + number2 + " = " + (number1 * number2));
    System.out.println(calculation);

}else if (operator.equals("/")){
    calculation = (number1 + " / " + number2 + " = " + (number1 / number2));
    System.out.println(calculation);

}else{
    calculation = operator + ":" + " Is not a valid operator!";
    System.out.println(calculation);

}

I think its maybe the ( . ) thats the problem, my output to console

Enter the operator you would like to choose(+, -, *, /): +
Enter the first number: 5.5
Enter your second number: 5.5
Only enter numbers not letters.
0.0 + 0.0 = 0.0

And now the int numbers that works fine.

Enter the operator you would like to choose(+, -, *, /): +
Enter the first number: 5
Enter your second number: 5
5.0 + 5.0 = 10.0
Solution

  • The regular expression "^[0-9]+$" only evaluates to true for integers, because it checks whether the string consists of 0 - 9. If you want to check for doubles as well, this might help: https://www.baeldung.com/java-check-string-number

    The first suggestion there is probably the easiest. Surround Double.parseDouble with a try catch, because it will give you an NumberFormatException if its not a number.