Java IF语句需要多个输入

Question

So I'm working on a four function calculator for java (yes I know I'm wasting my time, I'm just getting used/into java.) It takes the first two inputs fina and add/subtracts/etc them, and outputs that as an answer, and I attatched a while loop after that answer so the user can input as many more numbers as he would like.

while(finalanswer == 0){
        System.out.println("If finished, type 'done'.");
        System.out.println("To change your operation, type 'change'. Otherwise, enter your next number.");
        if(calc.next().equals("done")){
            finalanswer = 1; break;
        }else if(calc.next().equals("change")){
            System.out.println("'addition', 'subtraction', 'division', or 'multiplication'?");
            userOperation = calc.next();
        }else{
        modanswer = calc.nextDouble();
        if(userOperation.equals("addition")){
            System.out.println(answer += modanswer);
        }else if(userOperation.equals("subtraction")){
            System.out.println(answer -= modanswer);
        }else if(userOperation.equals("division")){
            System.out.println(answer /= modanswer);
        }else{System.out.println(answer *= modanswer);}
    }
    }

That is the loop that allows the user to add more inputs if he wants, but when I try and add a number I have to type two other numbers first (which have no effect as far as I've seen) and then the third number is finally input and added to the original answer.

Answer 1

Like Pshemo said, you have to store calc.next() before you check the different conditions:

String tmp = calc.next();

if(tmp.equals("done")){
      finalanswer = 1; break;
}else if(tmp.equals("change")){
      System.out.println("'addition', 'subtraction', 'division', or 'multiplication'?");
      userOperation = calc.next();
}else{
.
.
.

Answer 2

As explained briefly by Pshemo, the calc.next() function asks the user to input something, and returns the input. In this code, calc.next() is called three times in each cycle of the while loop. If the first input isn't "done", it continues. If the second input isn't "change", it continues, and the third input (obtained through calc.nextDouble() ) is assigned to modanswer .

You need to store the value of calc.next() as a separate variable to avoid having to read the input three times:

while(finalanswer == 0){
    System.out.println("If finished, type 'done'.");
    System.out.println("To change your operation, type 'change'. Otherwise, enter your next number.");
    String input = calc.next();
    if(input.equals("done")){
        finalanswer = 1; break;
    }else if(input.equals("change")){
        System.out.println("'addition', 'subtraction', 'division', or 'multiplication'?");
        userOperation = calc.next();
    }else{
    modanswer = Integer.parseInt(input);
...

Note that you need to use Integer.parsInt() to convert the String obtained through calc.next() into an Integer.