Think of our typical three users.

lbird

mjordan

tkukoc

Let's open accounts for them in our database.

Initial balances are 0 (zero).

burrowww.cs.indiana.edu% mysql -ua348 -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 677 to server version: 3.23.27-beta

Type 'help;' or '\h' for help. Type '\c' to clear the buffer

mysql> use a348
Database changed
mysql> show tables like "dgerman_BANK";
Empty set (0.01 sec)

mysql> create table dgerman_BANK (
    ->   username varchar(8),
    ->   balance float
    -> ); 
Query OK, 0 rows affected (0.00 sec)

mysql> insert into dgerman_BANK values (
    ->   'lbird', 0), ('mjordan', 0), ('tkukoc', 0);
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select * from dgerman_BANK;
+----------+---------+
| username | balance |
+----------+---------+
| lbird    |       0 |
| mjordan  |       0 |
| tkukoc   |       0 |
+----------+---------+
3 rows in set (0.01 sec)

mysql> exit
Bye
burrowww.cs.indiana.edu% 

#!/usr/bin/perl

use CGI;

$q = new CGI; 

$who = $q->param('which'); 

$amount = $q->param('amount'); 

print $q->header, $q->start_html; 

use DBI; 

my ($dsn) = "DBI:mysql:a348"; # data source name 
my ($username) = "a348";      # username
my ($password) = "a348AG";    # password
my ($dbh, $sth);              # database and statement handles
my (@ary);                    # array for rows returned by query

# connect to the database 

$dbh = DBI->connect($dsn, $username, $password, { RaiseError => 1 }); 

#issue query

$amount += 0; 

$dbh->do ("update dgerman_BANK set balance = balance + $amount where " . 
          "username = '$who'") if ($who); 

$sth = $dbh->prepare("select * from dgerman_BANK");  
$sth->execute(); 

print $q->startform; 

print "<table width=100%><tr> "; 

# read results of query, then clean up

while (@ary = $sth->fetchrow_array()) {

  # print join ("\t", @ary), "\n"; 
  $pic = $ary[0]; 
  $balance = $ary[1]; 

  print qq{    

    <td align=center valign=middle> 
    <input type="radio" name="which" value="$pic"> $pic <br> 
    <img src=
    "http://www.cs.indiana.edu/classes/a114/fall2001/lectures/nine/$pic.jpg">
    <br> Balance is: ($balance) </td> 

  }; 
}

$sth->finish(); 

print qq{ </tr> </table><p> 
  Enter amount: <input type="text" name="amount" size=4> then 
  push <input type="submit" value="Proceed"> 
  
}; 

$dbh->disconnect();

print $q->endform, $q->end_html; 

exit(0); 

Try it here. (How does this relate to the calculator, though? How is this different?)