Set amounts in database using php + form - php

Question

In my database users have a balance, im trying to set up a form that allows them to transfer amounts to each other. So for the from user it would - out of their current balance and update it to the new balance ( existing - amount transferred ) and for the receiver it would update ( existing + amount received ).
Heres my code below but its not updating any of the information:
<?php
if (isset($_POST['submit'])) {
$fromuser = $_POST['fromuser'];
$touser = $_POST['touser'];
$amount = $_POST['amount'];
$balanceto = mysql_query("SELECT `money` FROM `users` WHERE username = '$touser'");
$res1 = mysql_fetch_array($balanceto);
$balancefrom = mysql_query("SELECT `money` FROM `users` WHERE username = '$fromuser'");
$res2 = mysql_fetch_array($balancefrom);
$newmoney1 = ($res1['money'] + $_POST['amount']);
$newmoney2 = ($res2['money'] - $_POST['amount']);
$result1 = mysql_query("UPDATE `users` SET `money`='$newmoney1' WHERE username = '$touser'");
$result2 = mysql_query("UPDATE `users` SET `money`='$newmoney2' WHERE username = '$fromuser'");
}
?>
<form class="reg-page" role="form" action="" method="post">
<center>
Please note: Transfering funds is done at your own risk, please make sure you transfer the funds to the right person.<br><br>
<?php
$query = "SELECT username FROM users";
$result = mysql_query($query) or die(mysql_error());
$dropdown = "<div class='row'><div class='col-sm-6'><label>Transfer $ To<span class='color-red'> *</span></label><select name='touser' class='form-control margin-bottom-20'>";
while($row = mysql_fetch_assoc($result)) {
$dropdown .= "\r\n<option value='{$row['username']}'>{$row['username']}</option>";
}
$dropdown .= "\r\n</select></div><div class='col-sm-6'>
<label>Amount $<span class='color-red'> *</span></label>
<input type='text' name='amount' class='form-control margin-bottom-20'>
</div></div>";
echo $dropdown;
?>
<input type="hidden" value="<?php echo $user_data['username']; ?>" name="fromuser">
<button type="submit" class="btn-u">Transfer</button>
</center>
</form>
All help much appreciated.

Answer 1

$_POST does not contain submit because you never put a NAME tag on the submit button.
Instead of:
<button type="submit" class="btn-u">Transfer</button>
You need:
<button type="submit" class="btn-u" name="submit">Transfer</button>
See here:
How do I post button value to PHP?
On further reflection it's probably a good idea to talk about some of the problems here, let's start with this one:
$balanceto = mysql_query("SELECT `money` FROM `users` WHERE username = '$touser'");
$res1 = mysql_fetch_array($balanceto);
$balancefrom = mysql_query("SELECT `money` FROM `users` WHERE username = '$fromuser'");
$res2 = mysql_fetch_array($balancefrom);
This is duplicated code, you can move this into a function to avoid copying and pasting, which is good practice, and you can use that function in other places in your code when you need to get the balance. Formatting the structure correctly helps in the event that your table changes, and you need to update the SQL. Without this in a single place, you are going to climb all over your code to find all the changes and update them.
<input type="hidden" value="<?php echo $user_data['username']; ?>" name="fromuser">
This is very bad practice, as it makes it easy for someone to slip an extra variable into the header and submit whatever user they want to your code, transferring money out of any other account that they want. Since this page already has access to this variable:
$user_data['username']
You should be using this in the IF statement at the top, instead of submitting it along with the form.
<input type='text' name='amount' class='form-control margin-bottom-20'>
This is another problem. You are asking for an amount, but creating a text field. A better example of this would be:
<input type='number' name='amount' class='form-control margin-bottom-20'>
Again though, these are easily modifiable post values, you have to make sure to check again on the server to make sure you didn't get fooled:
if(!(isNumeric($_POST['amount']) || $_POST['amount'] == 0 || $_POST['amount'] == ''))
The code above checks to make sure you have a numeric value, and that it is not 0 or blank, both of which would be invalid inputs. If either of those values is submitted, then it errors out and sends the user back to the form without processing the update.
Later on in your code, you start a PHP Tag to create the drop down:
<?php
$query = "SELECT username FROM users";
$result = mysql_query($query) or die(mysql_error());
$dropdown = "<div class='row'><div class='col-sm-6'><label>Transfer $ To<span class='color-red'> *</span></label><select name='touser' class='form-control margin-bottom-20'>";
Assigning all of this to the $dropdown variable is completely wasted if you aren't going to use that drop down again (and it seems you are not). I can see that you wrapped it in PHP so you can loop over the options to print them out, but you can do that just as easily with a smaller PHP tag with a loop inside it, like this:
<select name='touser' class='form-control margin-bottom-20'>
<option value="null">Not Selected</option>
<?php
// Loop over all our usernames...
while($row = mysql_fetch_assoc($result)) {
// If we're not the current user...
if($row['username'] != $user_data['username']) {
// Add a drop down option!
echo "<option value='" . $row['username'] . "'>" . $row['username'] . "</option>";
}
}
?>
</select>
Note that this option ALSO includes a default "null" value for the select menu, and filters out the existing user (you can't transfer money to yourself, at least in this example). The null value is necessary because without it your code would automatically select the first user on the drop down list.
This would be my implementation of the same set of code here:
<?php
// If our submit is set...
if (isset($_POST['submit'])) {
// Get the balance for the from user
$fromBalance = getBalance($user_data['username']);
// Get the balance for the to user
$toBalance = getBalance($_POST['touser']);
// Get our new amounts, but don't do anything yet!
$newmoney1 = $toBalance + $_POST['amount'];
$newmoney2 = $fromBalance - $_POST['amount'];
// Check to make sure we have a valid amount
if(!(isNumeric($_POST['amount']) || $_POST['amount'] == 0 || $_POST['amount'] == '')) {
// Or error out!
echo 'ERROR: Bad amount Specified!';
// Check to make sure we have two valid users
} elseif($user_data['username'] == $_POST['touser']) {
// Or error out!
echo 'ERROR: Cannot transfer money to yourself!';
// Check to make sure sufficient funds are available
} elseif($newmoney2 < 0) {
// Or error out!
echo 'ERROR: Insufficient funds!';
// Check for default user selection...
} elseif($_POST['touser'] === 'null') {
// Or Error Out
echo 'ERROR: No username selected!';
// Otherwise we are good...
} else {
// So we call our update functions.
updateMoney($user_data['username'], $newmoney2);
updateMoney($_POST['touser'], $newmoney1);
// Send a success message
echo 'Transfer completed successfully, thank you!<br /><br />';
}
}
/** updateMoney()
*
* This function will take a user name and an amount and update their balance.
* Created to re-use code instead of copy and paste.
*
* #arg $user string
* #arg $amount integer
*/
function updateMoney($user, $amount) {
// Update our database table for this user with this amount
$result1 = mysql_query("UPDATE `users` SET `money`='$amount' WHERE username = '$user'");
}
/** getBalance()
*
* This function will return a balance for a given username.
* Created to re-use code instead of copy and paste.
*
* #arg $user string
* #return $amount integer
*/
function getBalance($user) {
// Execute query to get the result
$result1 = mysql_query("UPDATE `users` SET `money`='$amount' WHERE username = '$user'");
// Assign the result to a value
$res1 = mysql_fetch_array($balanceto);
// Return only the value we care about
return $res1['money'];
}
// Set our query for getting usernames from the DB
$query = "SELECT username FROM users";
// Get the usernames!
$result = mysql_query($query) or die(mysql_error());
?>
<form class="reg-page" role="form" action="" method="post">
<center>
Please note: Transfering funds is done at your own risk, please make sure you transfer the funds to the right person.
<br>
<br>
<div class='row'>
<div class='col-sm-6'>
<label>Transfer $ To<span class='color-red'> *</span></label>
<select name='touser' class='form-control margin-bottom-20'>
<option value="null">Not Selected</option>
<?php
// Loop over all our usernames...
while($row = mysql_fetch_assoc($result)) {
// If we're not the current user...
if($row['username'] != $user_data['username']) {
// Add a drop down option!
echo "<option value='" . $row['username'] . "'>" . $row['username'] . "</option>";
}
}
?>
</select>
</div>
<div class='col-sm-6'>
<label>Amount $<span class='color-red'> *</span></label>
<input type='number' name='amount' class='form-control margin-bottom-20'>
</div>
</div>
<button type="submit" class="btn-u" name="submit">Transfer</button>
</center>
</form>
But you STILL need to go fix the code so that you are NOT using MySQL and switch to MySQLi or PDO so that you can do prepared statements and actually protect yourself from MySQL injection attacks.
See here for more details:
https://wikis.oracle.com/display/mysql/Converting+to+MySQLi

Answer 2

You have posting the form with nameless button and trying to access via $_POST['submit']
<button type="submit" class="btn-u">Transfer</button>
name is missing. Add and try
<button type="submit" name="submit" class="btn-u">Transfer</button>

Answer 3

I think the button is missing tag 'name'. Try add this on your button:
<button type="submit" class="btn-u" name='submit'>Transfer</button>
To optimize your script I suggest do this:
if (isset($_POST['submit'])) {
$fromuser = $_POST['fromuser'];
$touser = $_POST['touser'];
$amount = $_POST['amount'];
$result1 = mysql_query("UPDATE `users` SET `money`= `money` + '$amount' WHERE username = '$touser'");
$result2 = mysql_query("UPDATE `users` SET `money`= `money` - '$amount' WHERE username = '$fromuser'");
}
So, you will eliminate two steps of processing and two hits on database.

Answer 4

start transaction
INSERT INTO power (sender, receiver, amount) VALUES ('$sender', '$receiver', '$amount')
UPDATE users SET power=power-$amount WHERE user_id='$sender'
UPDATE users SET power=power+$amount WHERE user_id='$receiver'

Answer 5

Submit button missing the name tag. use Transfer

Answer 6

Nothing glaringly wrong with the code, I'm assuming this is fake money.
Probably a malformed sql statement, try echoing the attempted sql before hand.
make sure all the queries work for a test example.