公式返回的值略低于"correct"答案？

好吧，我远非数学高手。哎呀，我记得足够多的高中代数来拼凑任何工作公式，这对我来说是一个胜利。因此，如果您在这里注意到一个不必要的冗长或令人困惑的公式，那就解释了。

但是，正如人们可以合理预期的那样，这里出了点问题。

我正在尝试制作一个简单的计算器，显示购买公交票与支付现金票价相比节省的成本。我很接近，但是我使用的公式的计算在某些情况下不起作用，我无法弄清楚原因。

在下面的示例中，基本区域和区域 4 按我的预期计算差异，而区域 1-3 返回的答案仅比正确答案低一点（即 $105.600000000000014 而不是 $106），区域 1 和区域 2 返回相同的答案，尽管公式不同。

我一直看着这个，直到我瞪大了眼睛。我相信答案很简单，但我看不出来。任何人？

感谢您的帮助。

代码如下：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Untitled Document</title>
<script language="javascript">
<!-- Begin Trip Tickets Savings Calc script
function  doMath4() {
    var one = parseInt(document.theForm4.elements[0].value);
    var two = parseInt(document.theForm4.elements[1].value);
    var selection = document.getElementsByName("zonett")[0].value;
    if(selection == "z4"){
        var prodZ4tt = (((one  *   two) * 4.25) *12) - (((one  *   two) * 3.75) *12);
        alert("Your yearly savings if you buy Trip Tickets is $"  +  prodZ4tt  +  ".");
    }
    else if(selection == "z3"){
        var prodZ3tt = (((one  *   two) * 3.75) *12) - (((one  *   two) * 3.35) *12);
        alert("Your yearly savings if you buy Trip Tickets is $"  +  prodZ3tt  +  ".");
    }
    else if(selection == "z2"){
        var prodZ2tt = (((one  *   two) * 3) *12) - (((one  *   two) * 2.8) *12);
        alert("Your yearly savings if you buy Trip Tickets is $"  +  prodZ2tt  +  ".");
    }
    else if(selection == "z1"){
        var prodZ1tt = (((one  *   two) * 2.5) *12) - (((one  *   two) * 2.3) *12);
        alert("Your yearly savings if you buy Trip Tickets is $"  +  prodZ1tt  +  ".");
    }
    else if(selection == "Base"){
        var prodBasett = (((one  *   two) * 1.5) *12) - (((one  *   two) * 1.5) *12);
        alert("Your yearly savings if you buy Trip Tickets is $"  +  prodBasett  +  ".");
    }
}
// End Trip Tickets Savings Calc script -->
</script>
</head>
<body>

<form name="theForm4" class="calcform">
<h2>You Do the Math: Commuter Express Trip Tickets Vs. Cash</h2>
<div class="calcform-content">
    <div class="formrow-calc">
      <div class="calcform-col1">
        <p>Days you commute on Commuter Express monthly:</p>
      </div>
      <div class="calcform-col2">
        <input type="text">
      </div>
      <div class="calcform-col3">&nbsp;</div>
    </div>
    <div class="clear"></div>

    <div class="formrow-calc">
      <div class="calcform-col1">
        <p>Daily boardings on Commuter Express Bus:</p>
        <table border="0" cellspacing="0" cellpadding="0" class="fareexampletable">
            <tr>
              <td colspan="2" class="savingsleft"><p class="ifyouride">EXAMPLE:</p></td>
              </tr>
            <tr>
              <td class="savingsleft"><p><strong>Go to work:</strong></p></td>
              <td class="savingsright"><p>1 time</p></td>
            </tr>
            <tr>
              <td class="savingsleft"><p><strong>Come home from work:</strong></p></td>
              <td class="additionline savingsright"><p>+1 time</p></td>
            </tr>
            <tr>
              <td class="savingsleft"><p><strong>Total:</strong></p></td>
              <td class="savingsright"><p>2 times</p></td>
            </tr>
          </table>
      </div>
      <div class="calcform-col2">
        <input type="text">
      </div>
      <div class="calcform-col3">&nbsp;</div>
    </div>
    <div class="clear"></div>

    <div class="formrow-calc savings-zone">
      <div class="calcform-col1">
        <p>Choose Zone:</p>
      </div>
      <div class="calcform-col2">
        <select name="zonett">
          <option value="Base">Base</option>
          <option value="z1">Zone 1</option>
          <option value="z2">Zone 2</option>
          <option value="z3">Zone 3</option>
          <option value="z4">Zone 4</option>
        </select>
      </div>
    </div>

    <div class="formrow-calc">

          <div class="calcform-col4-ce">

 <button type="submit" onclick="doMath4()" class="btn-submit"><div class="btn-submit"><img src="img/btn_savings.png" alt="Show My Yearly Savings" /></div></button> 

    </div>
    </div>
    <div class="clear">

</div>

</div>
</form>
</body>
</html>

这是我在评论中讨论的清理代码：

function  doMath4() {
    var one = parseInt(document.theForm4.elements[0].value);
    var two = parseInt(document.theForm4.elements[1].value);
    var selection = document.getElementsByName("zonett")[0].value;
    var m12 = one * two * 12;
    var prod = null;
    if(selection == "z4")
    {
        prod = (m12 * 4.25)  - (m12 * 3.75);
    }
    else if(selection == "z3")
    {
        prod = (m12 * 3.75) - (m12 * 3.35);
    }
    else if(selection == "z2")
    {
        prod = (m12 * 3) - (m12 * 2.8);
    }
    else if(selection == "z1")
    {
        prod = (m12 * 2.5) - (m12 * 2.32);
    }
    else if(selection == "Base")
    {
        prod = (m12 * 1.5) - (m12 * 1.5); //This is always 0?
    }
    if(prod != null)
    {
            prod = Math.round(prod);
        alert("Your yearly savings if you buy Trip Tickets is $"  +  prod  +  ".");
    }
}

您的问题的最简单解决方案包含在上面（和下面）：

prod = Math.round(prod);

这会将结果（prod）舍入到最接近的整数，无论它是什么。所以在你的例子中，$105.600000...将四舍五入为 106 美元，这是您要求的。

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