Code issue, don't know the right line of code

[dense tulip]

I've been studying java for the past 5 days and i tried to make a calculator today with the help of a tutorial, the tutorial made a calculator with two int variables, but i wanted to make a variable for the operator but i don't know what to change besides replacing the interger with char

package com.zerox51.test2.commands;

import org.bukkit.command.Command;
import org.bukkit.command.CommandExecutor;
import org.bukkit.command.CommandSender;

public class calcCommand implements CommandExecutor
{
@Override
public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {

    int numOfArguments = args.length;
    int value1 = Integer.parseInt(args[0]);
    char special = Character.parseChar(args[1]);
    int value2 = Integer.parseInt(args[2]);
    int sum = value1 special value2;

    sender.sendMessage ("Answer " + sum);




    return true;
}

}

Character.parseChar(args[1]); is not a real command and i dont know what kind of command could replace what i hoped worked.

[chilly cargo]

String#toCharArray -> char[]
String#charAt(int) -> char
Your special character in the center of your sum values won't work though

you need to parse the char i n a switch statement or map

[dense tulip]

Now that is alot of concepts i havent heard of yet.

[sacred tree]

https://stackoverflow.com/questions/3422673/how-to-evaluate-a-math-expression-given-in-string-form

[chilly cargo]

so too ways of doing this either switch

switch(special){
  '+' -> {
    // logic here
  }
  '-' -> {
    // logic here
  }
}

and so on

[cinder terrace]

You would have to map different values of special to operations, basically easiest way is
if special == +
sendMessage(val1+val2)

But there are some other ways also

[sacred tree]

    ScriptEngineManager mgr = new ScriptEngineManager();
    ScriptEngine engine = mgr.getEngineByName("JavaScript");
    String foo = "40+2";
    System.out.println(engine.eval(foo));```

[dense tulip]

give me a minute to try mentally consume this

[cinder terrace]

Cause essentially you wanna do sth different with val1 and val2 dependent on the special variable’s value

[dense tulip]

sth?

[cinder terrace]

Something

[dense tulip]

oh

if special == +
sendMessage(val1+val2) so i could do a bunch of if statements for eac operator?

[chilly cargo]

yea I reccomend using a switch here

for every operator

[sacred tree]

Just use teh built in JavaScript engin and it does it for you

was added in Java 1.6

[cinder terrace]

Yes but then you have the more sophisticated strategies like switch, or if you wanna use a map directly

[chilly cargo]

seems a bit overkill for doing something simple with 2 numbers

[sacred tree]

it will allow you to evaluate almost any math expression

[chilly cargo]

I mean won't an entire JavaScript parsing engine drag a little weight behind it thats not really needed for something this simple

[dense tulip]

ill look up a tutorial how switching works, thanks for the assistance.

[chilly cargo]

also its a good learning project 🙂

[cinder terrace]

The issue I see is the time and space inefficiency of using the js engine

[dense tulip]

woops didnt mean to do a reply

[sacred tree]

I guess it depends on how extensive he is going. if he's just making a simple abacus its a waste.

[cinder terrace]

Ye

[dense tulip]

ive been doing java for 5 days im just doing random things to learn basics.

[sacred tree]

Anythign more and its there so he may as well use it.

[chilly cargo]

if you are using a newer version of java consider using the nicer looking version of switch statement

this is clearer

switch(item){
 case 'x' -> {

 }
 defuault -> {

 }
}

vs

switch(item){
  case 'x':
    break;
  default:
    break;
}
``` if you need fall throughs the second method is just better though

[sacred tree]

with the JS engine you can do things like /sum (100/2.5)*10.4

[dense tulip]

I think i am using the latest

[sacred tree]

eg

[cinder terrace]

We also have libraries that do it but ye

[chilly cargo]

text parser is a nice starting project imo while I think using tools is nice its also very good to know how things work

[dense tulip]

I can't seem to get the switching to work properly

import org.bukkit.command.Command;
import org.bukkit.command.CommandExecutor;
import org.bukkit.command.CommandSender;

public class calcCommand implements CommandExecutor
{
    @Override
    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {

        int numOfArguments = args.length;
        int value1 = Integer.parseInt(args[0]);
        int value2 = Integer.parseInt(args[1]);
        int sum = 0;
         String special = value1 + "  " + value2;

        switch(special){
            case value1 + " + " + value2:
                sum = value1 + value2;
                break;
            case value1 + " - " + value2:
                 sum = value1 - value2;
                break;
            case value1 + " / " + value2:
                sum = value1 / value2;
                break;
            case value1 + " * " + value2:
                sum = value1 * value2;
                break;
        }
        sender.sendMessage("Answer " + sum);


        return true;
    }
}

I keep getting java: constant string expression required on all cases

[chilly cargo]

Special is just supposed to be the sign

You are making it val1 plus val2

Than you are changing it again in the cases

Your case should look like this

case "/":
case "+" etc

No logic can or should be done in the cases

[dense tulip]

import org.bukkit.command.Command;
import org.bukkit.command.CommandExecutor;
import org.bukkit.command.CommandSender;

public class calcCommand implements CommandExecutor
{
    @Override
    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {

        int value1 = Integer.parseInt(args[0]);
        int value2 = Integer.parseInt(args[1]);
        int sum = 0;

                 ;

        switch(){
            case "+":
                sum = value1 + value2;
                break;
            case "-":
                 sum = value1 - value2;
                break;
            case " % ":
                sum = value1 % value2;
                break;
            case " * ":
                sum = value1 * value2;
                break;
        }
        sender.sendMessage("Answer " + sum);


        return true;
    }
}```

I just don't see overall how switch statements work, i cant seem them to trigger when doing /calc 1 + 1 it just throws me a error but doing /calc 1 1 gives me 0 so somehow i cant get the switch statement to trigger @chilly cargo

[chilly cargo]

becuase your not switching anything

so you aren't getting an output

how is the code supposed to know what sign it is if your not providing it with an option to dictate such

[dense tulip]

you mean when i removed the special from the switch?

[chilly cargo]

yes I'd do something like this for a simple calculator
int value1 = Integer.parseInt(args[0]);
String sign = args[1];
int value2 = Integer.parseInt(args[2]);

i trust you could figure out logic with this

[dense tulip]

Oh

wait why does 2 have arg 0?

[chilly cargo]

now if you wanted to get more complex you'd want a better parser e.g. this wouldn't support something like 1+1+1 would be more complex

[dense tulip]

i just want two numbers

and a operator

[chilly cargo]

than what I provided should work fine as inputs