Doubts in the use of int variables

Question

I'm trying to do something really stupid, but maybe it will be my careless mistake ... In short, how is it possible that in a simple function like this:

function limitFunc(name){
  var domain=prompt(`Inserisci il dominio della funzione`);
  var sx=domain-0.2;
  var dx=domain+0.2;
  console.log(`sx`,sx, `dx:`,dx);
  //console.table(graph.limitCalculation(name, domain));
}

If I then write 1 with the prompt, the dx variable then calculated gives me a number multiplied by 10.

For example if I write 1: chrome console

Thanks for the help anyway

`prompt()` always returns a string, so you have to convert those values to numbers before doing math (especially `+`). — Pointy, Jun 01 '22 at 14:19
You should first convert `domain` to a number, you are working with a string (which has a different meaning for the `+` operator) — UnholySheep, Jun 01 '22 at 14:19
`"1" + 0.2` = `"10.2"`. `1 + 0.2` = `1.2` (approximately, but due to floating point math it might not be exactly 1.2) — WOUNDEDStevenJones, Jun 01 '22 at 14:20

score 1 · Accepted Answer · answered Jun 01 '22 at 14:22

prompt returns a string.

All you need to do is convert your string into a number, basically:

function limitFunc(name) {
    let domain = prompt(`Inserisci il dominio della funzione`);
    domain = +domain; // converted string into number
    const sx = domain - 0.2;
    const dx = domain + 0.2;
    console.log(`sx:`, sx, `dx:`,dx);
}

limitFunc();

Obviously, you'd want to check if the user prompts a valid answer (i.e. a number).

Doubts in the use of int variables

1 Answers1