I have problem with my checkbox validation on my Tip Area Soccer Game. So if the user likes to tip a game, he must have to use 2 inputs field and the confirmation checkbock. But if the user uses 2 inputs fields and "more than one" confirmation checkbox, then he must get an alert error message. Because the right combination consists from "2 input fields + confimration checkbox" Here, in my screenshot you see the right combination for the green submit button:

And in the second screenshot you see the error combination:

I don't have any idea of how to code the alert for the error message on the display if the user uses the second combination.
Here's my Javascript code:
function chkAddTip(){
var inputs = document.getElementById('AddTip').getElementsByTagName('input');
// boolean flag
var foundValid = false;
// early exit the loop if at least one valid bet has been found
for (var i = 0; i < inputs.length && !foundValid; i += 3){
if (inputs[i].type !== "submit" && (inputs[i].value && inputs[i + 1].value && inputs[i + 2].checked)) {
// set the flag to true when a valid bet is found
foundValid = true;
}
}
// determine the return value depending on the flag
if (foundValid) {
return true;
}
else {
alert("Bitte deinen Tipp und die Bestättigung abgeben.")
inputs[0].focus();
return false;
}
And here my form code:
<form action="Ctipservlet" id="AddTip" onsubmit="return chkAddTip()" method="POST">
<div id="inhalt"><h1>Tip Area</h1>
<table>
<tbody>
<tr>
<th>Playdate</th>
<th>Playtime</th>
<th>Games</th>
<th>Your Tip</th>
<th>Confirmation</th>
</tr>
<tr>
<td>21.07.</td>
<td>19:30 Uhr</td>
<td>Schalke - Bayern</td>
<td><input style="width:30px!important; text-align: center;" type="text" name="team_a0" maxlength="2" size="2">:<input style="width:30px!important; text-align: center;" type="text" name="team_b0" maxlength="2" size="2"></td>
<td><input type="checkbox" name="check0"></td>
</tr>
<tr>
<td>22.07.</td>
<td>20:30 Uhr</td>
<td>Dortmund - Leverkusen</td>
<td><input style="width:30px!important; text-align: center;" type="text" name="team_a1" maxlength="2" size="2">:<input style="width:30px!important; text-align: center;" type="text" name="team_b1" maxlength="2" size="2"></td>
<td><input type="checkbox" name="check1"></td>
</tr>
<tr>
<td>23.07.</td>
<td>15:30 Uhr</td>
<td>Wolfsburg - Nürnberg</td>
<td><input style="width:30px!important; text-align: center;" type="text" name="team_a2" maxlength="2" size="2">:<input style="width:30px!important; text-align: center;" type="text" name="team_b2" maxlength="2" size="2"></td>
<td><input type="checkbox" name="check2"></td>
</tr>
</tbody>
</table>
<input class="button_green" type="submit" name="tip" value="Submit Tip">
<input class="button_blue" onclick="this.form.onsubmit = null" type="submit" name="back" value="Back">
</div>
</form>
I hope someone have idea for this checking