Convert String to Float

Question

Convert String to Float

Asked 5 years, 4 months ago

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I’m trying to convert string to float to calculate the advantage between gasoline and ethanol, but is not returning result in Screen.

Below the code HTML and JS:

var etanol, gasolina;

function Vantagem(){
	etanol = parseFloat(txtEtanol.value.replace(",","."));
	gasolina = parseFloat(txtGasolina.value.replace(",","."));

	if (etanol < 0.7 * gasolina) {
		document.getElementById('status').src="img/medidorEtanol.jpg";

	} else{
		document.getElementById('status').src="img/medidorGasolina.jpg";
	}
}

function Limpar(){
	document.getElementById('status').src="img/medidorNeutro.jpg";
}

<!DOCTYPE html>

<html>

	<head>
		<meta charset = 'UTF-8'>

		<title> Calculadora de Combustível </title>


	</head>

	<body>

		<header>

			<h1> Calculadora de Combustível </h1>
	

		</header>

		<img src='img/medidorNeutro.jpg' id="status">


		<form name="frmFlex">

			Etanol: <input type="text" name="txtEtanol" placeholder="Etanol"> <br/>
			Gasolina: <input type="text" name="txtGasolina" placeholder="Gasolina"> <br/>

			<button onclick="Vantagem()"> Vantagem </button> <br/>
			<button onclick="Limpar()"> Limpar </button> <br/>

		</form>
    
    
			<script type="text/javascript" src="script.js"></script>

	</body>

</html>

Use the method etanol = +txtEtanol.value.replace(",",".");
 gasolina = +txtGasolina.value.replace(",",".");

 instead of parseFloat

– Maury Developer

2019/07/21 at 21:05

1 answer

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by Ricardo Pontual • **21,129** points · Answer 1 · 2019-07-21T21:03:56+00:00

Your code has some problems:

on the line etanol = parseFloat(txtEtanol.value.replace(",","."));, where the variable was defined txtEtanol?
in its input, it would not be better to define "txtEtanol" as id in place of name?
why declare the global variables var etanol, gasolina; if you’re only using in Function?
to compare and ensure operation with gasoline, add a parenthesis here: if (etanol < 0.7 * gasolina)

To simplify a little bit the code, I created this example:

function Vantagem() {
    var etanol = parseFloat(document.getElementById('txtEtanol').value.replace(",", "."));
    var gasolina = parseFloat(document.getElementById('txtGasolina').value.replace(",", "."));

    if (etanol < (0.7 * gasolina)) {
        document.getElementById('status').src = "img/medidorEtanol.jpg";
        alert('medidorEtanol'); // apenas para testar

    } else {
        document.getElementById('status').src = "img/medidorGasolina.jpg";
        alert('medidorGasolina'); // apenas para testar
    }
}

function Limpar() {
    document.getElementById('status').src = "img/medidorNeutro.jpg";
}

<header>
   <h1> Calculadora de Combustível </h1>
</header>
<img src='img/medidorNeutro.jpg' id="status">

   Etanol: <input type="text" id="txtEtanol" placeholder="Etanol"> <br/>
   Gasolina: <input type="text" id="txtGasolina" placeholder="Gasolina"> <br/>
   <button onclick="Vantagem()"> Vantagem </button> <br/>
   <button onclick="Limpar()"> Limpar </button> <br/>