Java中的If-Else问题

Question

I am doing a conditional statement in javascript. When the user enters a value in the input box "Collect", its value together with the value from input box "CurBal" will perform an addition and put the answer in the input box named "Balance".

If the user enters a value in the input box "Deposit", its value will be substracted from the "CurBal" and the difference will also be reflected (supposedly) in the "Balance"

I have this code:

var collect = parseFloat(document.getElementById("Collect").value) ||0;
var dep     = parseFloat(document.getElementById("Deposit").value) ||0;
var curr    = parseFloat(document.getElementById("CurBal").value) ||0;
var bal     = document.getElementById("Balance");

if (collect.value = true)
{
 bal.value = (collect + curr).toFixed(2)
 bal       = document.getElementById("Balance");
}

else if (dep.value = true)
{
 bal.value = (curr - dep).toFixed(2)
 bal       = document.getElementById("Balance");
} 

The HTML:

<tr>
 <td> &nbsp;Collections: </td>
 <td> &nbsp; <input onchange="addNumbers()" type="text" id="Collect" name="Collect" value="" /> </td>
</tr>

<tr>
 <td> &nbsp;Deposits:</td>
 <td> &nbsp;<input onchange="addNumbers()" type="text" id="Deposit" name="Deposit" value="" /> </td>
</tr>

<tr>
 <td> &nbsp;Current Balance: </td>
 <td> &nbsp;<input onchange="addNumbers()" type="text" id="CurBal" name= "CurBal" value="<?php echo $all['balance']; ?>" readonly="readOnly" /> </td>
</tr>

<tr>
 <td> &nbsp;Balance: </td>
 <td> &nbsp;<input type="text" id="Balance" name="Balance" value="" readonly="readOnly" /> </td>
</tr>

But, its just performing the first condition correctly. If I entered a value in the input box "Deposit", it isn't subtracting the value from "CurBal", its just copying the value from "CurBal".

What should be removed or added or changed? Thank you for the help

Additional info: The user can only EITHER enter a value to "Collect" OR "Balance".

Answer 1

EDITED PER COMMENTS BELOW

// Collect is now a number
var collect = parseFloat(document.getElementById("Collect").value) ||0;

// dep is now a number
var dep     = parseFloat(document.getElementById("Deposit").value) ||0;

// Cur is now a number
var curr    = parseFloat(document.getElementById("CurBal").value) ||0;

// bal is now pointing to an element
var bal     = document.getElementById("Balance");


// What are you trying to compare here? That bal !== 0 perhaps?
// Collect is a number, so we can do the compare here.
if (collect !== 0)  {
 bal.value = (collect + curr).toFixed(2)


 // Dep, on the other hand, is pointing to an element
 // so we use the property here
 // The leading '+' is a quick way to turn the string value (dep.value is a string)
 // into a number.
} else if (+dep.value !== 0) {
 bal.value = (curr - dep).toFixed(2)
}

** Notes ** The line:

if (collect !== 0)  {

can be written shorter as

if (collect)  {

but I always recommend writing the most readable version that describes exactly what you mean.

Answer 2

You have this:

if (collect.value = true)
{
 bal.value = (collect + curr).toFixed(2)
 bal       = document.getElementById("Balance");
}

else if (dep.value == true)
{
 bal.value = (curr - dep).toFixed(2)
 bal       = document.getElementById("Balance");
} 

It sounds as though you need this:

if (collect.value = true)
{
 bal.value = (collect + curr).toFixed(2)
 bal       = document.getElementById("Balance");
}

if (dep.value == true)
{
 bal.value = (curr - dep).toFixed(2)
 bal       = document.getElementById("Balance");
}

You have an else if condition, so if collect.value is true, your other conditions won't run.

Of note - you also are performing assignment in your if statements, when in fact, you should be checking for equality. In fact, you don't even need to do that; you can do:

if (collect.value)
{
...
}

if (dep.value)
{
...
} 

Answer 3

You are assigning true to collect.value in the first if test. The value of an assignment expression is the value assigned; in this case true . Thus the first test will always succeed. You should use == or === for comparison tests. (The first operator will convert types if necessary; the === operator will only succeed if the current data types are already the same).

For boolean values, it's better to use if (collect.value) (etc.) rather than if (collect.value == true) .

Answer 4

you are missing double equal sign in if condition. try changing the condition.

if (collect.value != 0)

else if (dep.value != 0)

Answer 5

Try this

var collect = parseFloat(document.getElementById("Collect").value) ||0;
var dep     = parseFloat(document.getElementById("Deposit").value) ||0;
var curr    = parseFloat(document.getElementById("CurBal").value) ||0;
var bal     = document.getElementById("Balance");

if (collect != 0)
{
 bal.value = (collect + curr).toFixed(2)
 bal       = document.getElementById("Balance");
}

else if (dep != 0)
{
 bal.value = (curr - dep).toFixed(2)
 bal       = document.getElementById("Balance");
}