Ask Me Help Desk - I cannot understand a part of javascript function saldot()

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">

<html>
<script language="javascript">

/// Start of Pincode length Validation ///
function pinlen()
{
var n;
n=f1.t1.value;
if(n.length<7)

{
f1.t1.value="";
f1.t1.focus();
return false;
}
return true;
}

/// Start of Pincode Character validaion ///
function pinchar()
{
var n,i,ch;
n=f1.t1.value;
for (i=0;i<n.length;i )
{
ch=n.charAt(i);

if(isNaN(ch)==true)
{
f1.t1.value="";
f1.t1.focus();
return false;
break;
}}
return true;
}

///Start of Salary Character ///
function salchar()
{
var n,i,ch
n=f1.t2.value;
for(i=0;i<n.length;i )
{
ch=n.charAt(i);

if(isNaN(ch)==true && ch!=".")
{
f1.t2.value="";
f1.t2.focus();
return false;
break;
}}
return true;
}
///Start of Salary dot ///
function saldot()
{
var n,i;
n=f1.t2.value;
for (i=0;i<n.length;i )
{
ch=n.substring(i,i 1);
if(ch==".")
{
cnt=n.substring(i,n.length);
if(cnt.length>3)
{f1.t2.value="";
f1.t2.focus();
return false;
break;
}}}
return true;}
//// Varification steps ////
function chk()
{
if(!pinlen())
alert ("pincode should not be less tha 6");
else
{
if(!pinchar())
alert ("not a character");
else
{
if(!salchar())
alert ("Salary contains invalid Character");
else
{
if(!saldot())
alert ("Salary contains only 2 digits after dot");
else
{
alert("pincode 7 salary valid");
}}}}}

</script>

<body>

<form name="f1">
<h1><center>Validation of Pincode & Salary</center></h1>

Enter the pincode
<input type="text" name="t1" maxlength="10"><p>

Enter the salary
<input type="text" name="t2" maxlength="10"><p>
<input type="button" name="b1" value="click" onClick="chk()"><p>


</body>
</html>