How can I make a field become mandatory if a certain drop down selection is made?

[mlshoats]

Hello I am trying to make a log to track questions i answer on little hardware problems. I got most of it working but I am very new to programming anything and just started picking up things. I am trying to figure out how to make it that if I select "Other" from either one of my drop downs that it makes the "Comment" text box mandatory. One of my friends said it was easy but I can't figure it out at all. PLEASE HELP.

Here is everything I have so far. Thank you in advance.

<table>
  <tbody>
    <tr>
        <td>
    <input type="button" name="<? echo $lc_name;?>_start_button"  id="<? echo $lc_name;?>_start_button" onclick="javascript:timeButton('<? echo $lc_name;?>_start');"  value="Start Call"/>
  <input type="text" readonly="true" name="start_time" id="<? echo $lc_name;?>_start_time" /><br />
            <label for="cname">Caller:</label>
            <input tabindex="1" name="cname" type="text"
            onkeypress="return handleEnter(this, event)"><br>
 
            <label for="deptCD">Dept Code:</label>
            <select name="deptCD" tabindex="4"
            onkeypress="return handleEnter(this, event)">
            <option selected="selected" value="99">Select Dept Code</option>
                <? echo $_SESSION[$dynadeptCD]; ?>
            </select><br>
 
            <input type="hidden" name="assocN"
            value="<?PHP echo  $_SESSION['fName']." ".$_SESSION['lName']; ?>" />
 
            <label for="resCD">Res Code:</label>
            <select name="resCD" tabindex="9"
            onkeypress="return handleEnter(this, event)">
                <? echo $_SESSION[$dynaresCD]; ?>
            </select><br>
 
            <label for="resCD2">Res Sup:</label>
            <select name="resCD2" tabindex="9"
            onkeypress="return handleEnter(this, event)">
            <option selected="selected" value="99">Select Sup Code</option>
                <? echo $_SESSION[$dynaresCD2]; ?>
            </select><br>
              <label for="unnecessary">Unnecessary</label>
            <input value="1" name="unnecessary" id="<?PHP echo $lc_name; ?>_CallLog_unnecessary" type="checkbox"  tabindex="11"> <label for="followUP">Follow Up</label>
            <input value="1" name="followUP" id="<?PHP echo $lc_name; ?>_CallLog_followUP" type="checkbox"  tabindex="11"><br />
            <input value="Submit" name="<? echo $lc_name;?>_end_button" type="submit" tabindex="12"  
            id="<? echo $lc_name;?>_end_button"    
            onkeypress="return handleEnter(this, event);" />
            <input value="Reset" name="reset" type="reset"  tabindex="13"
            onclick="clearit('<?PHP echo $lc_name; ?>_start');"
            onkeypress="return handleEnter(this, event)" style="float:right"><br>
        </td>
 
            <td >
  <input type="hidden" name="new_call_id" id="new_call_id" value="<? echo md5(uniqid(time()));?>" />
    <input type="hidden" name="end_time" id="<? echo $lc_name;?>_end_time" value="" />
            <label for="comment">Enter A Comment:</label>
            <textarea name="comment" cols="35" rows="14" id="comment"  tabindex="10"
            onfocus="javascript:this.form.comment.focus();this.form.comment.select();"
            > </textarea>
 
            <input value="<?PHP echo $nav; ?>" name="nav" type="hidden">
            <input value="CallLog" name="section" type="hidden">
            <input type="hidden" name="sourceID" value="<?PHP echo $uc_name; ?>">
        </td>
    </tr>
  </tbody>
</table>

[acoder]

Welcome to TSDN!

You will probably want to check when the form is submitted. Call the validation function onsubmit, e.g. [HTML]<form ... onsubmit="return yourValidationFunction();">[/HTML] In the validation function, check the value of the dropdown. If the value is selected, then check the value of comments field. If it is empty then return false.

Check out some of the links in the Offsite Links thread on form validation.