What's the difference between: char nchar varchar nvarchar

1. char and varchar are both character data types.
2. The difference is that char is fixed length and varchar is variable length. 
3. Use char when the sizes of the column data entries are consistent or similar, for example,  city code or phone number. 
4. Use varchar when the sizes of the column data entries vary considerably, e.g. shipping addresses, URL, so that a shorter value takes less space than a longer one.
5. nchar and nvarchar are similar to char and varchar, but they are used to store Unicode data (using the UNICODE UCS-2 character set)

Javascript for blocking numbers

<script language="javascript" type="text/javascript">

function blockNonNumbers(obj, e, allowDecimal, allowNegative) {

var key;
var isCtrl = false;
var keychar;
var reg;
if (window.event) {key = e.keyCode;
isCtrl = window.event.ctrlKey
}

else if (e.which) {key = e.which;
isCtrl = e.ctrlKey;
}

if (isNaN(key)) return true;keychar = String.fromCharCode(key);

// check for backspace or delete, or if Ctrl was pressedif (key == 8 || isCtrl) {
return true;}
reg = /\d/;

var isFirstN = allowNegative ? keychar == '-' && obj.value.indexOf('-') == -1 : false;
var isFirstD = allowDecimal ? keychar == '.' && obj.value.indexOf('.') == -1 : false;
return isFirstN || isFirstD || reg.test(keychar);}
</script>
<div class="floatl width320"><div class=" left_part">effective from:<span class="colorred">*</span></div><div class="right_part"><asp:TextBox ID="txtEffectiveFrom" runat="server" class="textbox"></asp:TextBox><img alt="Calendar" src='<%=Page.ResolveClientUrl("App_Themes/images/meal_booking_datepicker.png") %>'onclick="javascript:displayCalendar(document.getElementById('<%=txtEffectiveFrom.ClientID%>'),'mm/dd/yyyy',this);"id="imgfrom" class="margintop-3" /></div></div>

Javascript For trimming the whitespace and to check the white spaces

Below script is to validating the blank fields:
<script language="javascript" type="text/javascript"

>function isBlank(s) {
if (s == null)
return true;
if (s.match(/^\s*$/)) {
return true}return false;}

function trim(str, chars) {
return ltrim(rtrim(str, chars), chars);}

function ltrim(str, chars) {chars = chars ||
"\\s";
return str.replace(new RegExp("^[" + chars + "]+", "g"), "");}

function rtrim(str, chars) {chars = chars ||
"\\s";
return str.replace(new RegExp("[" + chars + "]+$", "g"), "");}

</script>

e.g:
if (isBlank(trim(objPrice.value, ' ')) || trim(objPrice.value, ' ').length == 0) {
alert(
"Please enter Price.");document.getElementById(price).focus();

return false;}

Move Values from one list box to another

<script language="javascript" type="text/javascript">

function listbox_moveacross(sourceID, destID) {
var str = '';
var src = document.getElementById(sourceID);
var dest = document.getElementById(destID);
var j = 0;
for (var count = 0; count < src.options.length; count++) {
if (src.options[count].selected == true) {j++;
}
}

if (j > 2) {alert(
"Maximum 2 Week Of Day you can select")
return false;}

else {
for (var count = 0; count < src.options.length; count++) {
if (src.options[count].selected == true) {
var option = src.options[count];
var newOption = document.createElement("option");newOption.value = option.value;
newOption.text = option.text;
newOption.selected =
true;
if (str.length == 0) {str = option.value;
}

else {str = str +
"," + option.value;}

try {dest.add(newOption,
null); //Standardsrc.remove(count, null);}
catch (error) {dest.add(newOption);
// IE onlysrc.remove(count);
}
count--;
}
}
str = '';
var list = document.getElementById('<%=lstWeekOffDays.ClientID %>');
for (var count = 0; count < list.options.length; count++) {
var option = list.options[count];
var newOption = document.createElement("option");newOption.value = option.value;
newOption.text = option.text;
newOption.selected =
true;
if (str.length == 0) {str = option.value;
}

else {str = str +
"," + option.value;}
}
document.getElementById(
'<%=hdnWeekOffDays.ClientID %>').value = str; }
}

</script>
<table><tr><td><asp:ListBox ID="lstWeekDays" SelectionMode="Multiple" runat="server"></asp:ListBox></td><td><table><tr><td>
<input type="button" class="btnHyperlink" id="HyLeft" value=">>" onclick="listbox_moveacross('<%=lstWeekDays.ClientID %>','<%=lstWeekOffDays.ClientID %>')"; />　
</td></tr><tr><td><input type="button" class="btnHyperlink" id="HyRight" value="<<" onclick="listbox_moveacross('<%=lstWeekOffDays.ClientID %>','<%=lstWeekDays.ClientID %>')"; /></td></tr></table></td><td><asp:ListBox ID="lstWeekOffDays" SelectionMode="Multiple" runat="server"></asp:ListBox></td></tr><tr><td><asp:Button runat="server" ID="btnSubmit" Text="Submit" OnClick="btnSubmit_Click" /></td></tr><asp:HiddenField ID="hdnWeekOffDays" runat="server" /></table>