Need help with + - * / calculator

[Aconitum]

I'm new to java, and trying to make just a basic calculator, I want the calculator to be able to cycle through options till the desired math function is found, then used. It doesn't seem to work so help would be appreciated.
This is my code so far:

import java.util.Scanner;

public class calculator {
	public static void main(String args[]) {
		Scanner input = new Scanner(System.in);
		double fnum, snum, answer;
		String name = input.nextLine();
		System.out.println("Do you want to add?");
		name = input.nextLine();
		if (name == "yes") {
			System.out.println("Please enter first number:");
			fnum = input.nextDouble();
			System.out.println("Please enter second number:");
			snum = input.nextDouble();
			answer = fnum + snum;
			System.out.println(answer);
		} else {
			System.out.println("okay");
		}
		System.out.println("Do you want to subtract?");
		name = input.nextLine();
		if (name == "yes") {
			System.out.println("Please enter first number:");
			fnum = input.nextDouble();
			System.out.println("Please enter second number:");
			snum = input.nextDouble();
			answer = fnum - snum;
			System.out.println(answer);
		} else {
			System.out.println("okay");

		}
		System.out.println("Do you want to multiply?");
		name = input.nextLine();
		if (name == "yes") {
			System.out.println("Please enter first number:");
			fnum = input.nextDouble();
			System.out.println("Please enter second number:");
			snum = input.nextDouble();
			answer = fnum * snum;
			System.out.println(answer);
		} else {
			System.out.println("okay");
		}
		System.out.println("Do you want to divide?");
		name = input.nextLine();
		if (name == "yes") {
			System.out.println("Please enter first number:");
			fnum = input.nextDouble();
			System.out.println("Please enter second number:");
			snum = input.nextDouble();
			answer = fnum / snum;
			System.out.println(answer);
		} else {
			System.out.println("okay");
		}

	}
}

[awinston]

When comparing strings for equality, you want to use this:

String1.equals(String2)

The == operator should only be used to check if primitive data types are equal. When applied to objects, it checks if the two references point to the same object.

[Aconitum]

So where would I put that in my code? (Sorry I'm new to all of this)

[Fubarable]

I'm new to java, and trying to make just a basic calculator, I want the calculator to be able to cycle through options till the desired math function is found, then used.

Whenever I see something like this -- a desire to cycle through code -- I automatically think of using a loop of some sort, here a while loop where you keep looping until the user gives you a valid reply.

It doesn't seem to work so help would be appreciated.

You'll want to give us as detailed a description of what it is doing or not doing as it will greatly help us help you.

This is my code so far:

import java.util.Scanner;

public class calculator {
	public static void main(String args[]) {
		Scanner input = new Scanner(System.in);
		double fnum, snum, answer;
		String name = input.nextLine();
		System.out.println("Do you want to add?");
		name = input.nextLine();
		if (name == "yes") { // ******

An immediate big issue I see on quick scan of your code is that you're comparing Strings using ==. Don't do that is this checks if one String variable refers to the exact same object as another String variable (or literal) which is not what you really want to do. Instead you want to make sure that the two Strings contain the same characters in the same order, and so you'll want instead to use either the equals(...) or equalsIgnoreCase(...) methods.

[Aconitum]

I understand, but still have no idea how to change my code... :(

[gnarkill10]

pretty sure you need to put the string inside the curly braces bro, might be wrong though. Can someone confirm this

else {
System.out.println("okay");
}
System.out.println("Do you want to subtract?");
name = input.nextLine();

if (name == "yes") {
System.out.println("Please enter first number:");
fnum = input.nextDouble();
System.out.println("Please enter second number:");
snum = input.nextDouble();
answer = fnum - snum;
System.out.println(answer);
}

[awinston]

I understand, but still have no idea how to change my code... :(

Do you know how to use a while loop? If not, learn here: While Loops

As for fixing your comparison of Strings, you would just have to replace your current boolean conditions involving the == operator with boolean conditions using the .equals() method.

[gnarkill10]

this might help bro, Bucky is so helpful!

Java - 7 - Building a Basic Calculator

[Aconitum]

I have done this

if (name.equalsIgnoreCase(name)) {

But I don't know how to take it so it satisfies as a yes or no answer

[Aconitum]

okay I solved it by changing it to:

if (name.equalsIgnoreCase("Yes")) {

My last problem is I have to type something in the console to start the program, how can I make the program start automatically?

[awinston]

I have done this

if(name.equalsIgnoreCase(name)) {

But I don't know how to take it so it satisfies as a yes or no answer

Firstly, you don't want to check if the content of variable name is equal to the content of variable name because this will always be true. You want to check if the content of variable name is equal to "yes".

Secondly, if the boolean expression evaluates to true, then that means that the person entered "yes". If the boolean expression evaluates to false, then the person entered something other than yes (which in this case means "no"). This boolean expression provides you with a yes/no question.

[Fubarable]

okay I solved it by changing it to:


My last problem is I have to type something in the console to start the program, how can I make the program start automatically?

Please use [code] [/code] tags not quote tags around your posted code in this forum.

As for your last statement what exactly do you mean? How will the program magically start if you don't tell the operating system to run it? I think you need to type in "java your program name" for it to run.

[Aconitum]

I mean, to run in eclipse's console I have start the program which is fine, but then type something to start the code sequence, is there a way to start the code without doing that?

[awinston]

I mean, to run in eclipse's console I have start the program which is fine, but then type something to start the code sequence, is there a way to start the code without doing that?

On line 7 of your code, you demand input for seemingly no reason. If you remove that line, then the program should automatically ask if you want to add.

Edit: But you must initialize variable name somewhere else!

[Aconitum]

No, because that is what defines the name variable, without that line it doesn't work.

[Aconitum]

Where else can I initialize it?

[awinston]

Yes, I caught that and edited my previous post. You must initialize it somewhere else. In fact, you can just change line 7 to this:

String name;

[Aconitum]

Thank you, for god sake another problem! The answer counts as an answer for the next statement. Any ideas?

[awinston]

Just to clarify, I used some wrong terminology. When I said initialize, I meant to say define. Initializing a variable involves actually assigning a value to a variable.

[awinston]

Thank you, for god sake another problem! The answer counts as an answer for the next statement. Any ideas?

I'm not sure what you mean. Could you clarify?