What r the values of for loop and if statement?

arbab · June 16th, 2011, 02:00 AM

Hi!

I have written the following program from a book, this program is basically for an exception, first I donât understand the follow of this program, specially the values in for loop and in if statement, secondly the only output is this script and nothing is happening, in Red I am writing what I understand and after the program I have few questions:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html><head><title>Exception test</title>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<script language="Javascript">
function primeTest(n)
{
document.write ("Testing"+n+":")
try{
if (n<1 || n>20) throw "It's out of range" //n is less than 1 or greater than 20
for(var i =2; i <n; ++i) //I is equal to 2 increment in I till I is less than n
if (n% i ==0) throw "It's divisible by"+ //n divide by 0 reminder 0, then "It's divisible by"
document.writeln("It's prime. <br>") //if 0 then its prime
}
catch(exception){ //otherwise catch
document.writeln(exception+'<br>') //Write exception
}
}
</script>
<meta content="MSHTML 6.00.2900.6082" name="GENERATOR"></head>
<body>
<p>this script </p>
<script language="javascript">
<!-
for(i=0;i<=21;++i) //this is comment
{
primeTest(i)
}
-></script>
</body></html>

Questions:
1-At 1st what is the value of n? Since we have not declared it?
2-The 1st value of I is 2?

Thanks in advance

disel2010 · June 16th, 2011, 04:32 AM

Hi arbab,

1> the value of n is what you pass to it in the for loop: primeTest(i) and the for loop goes from zero to twenty-one
2> the value of i in the for loop goes from zero to twenty-one, so the frist value is zero (the increment only happens at the end of the for loop)
2> but wait... they have declared a new i within the primeTest function... this (function-scope) variable i starts indeed at two

arbab · June 27th, 2011, 05:11 PM

Primetest is the function which takes n as argument, but n is used within the function of primetest, so is it n 1st calculated from primetest function then gives value to primetest function.

Please explain one flow of the program, I still donât get when the exception will be thrown and catch?

disel2010 · June 29th, 2011, 06:44 AM

Hi,

- the primeTest is called 22 times (from i=0 up to i = 21)
- in its first and last call (so when i = 0 and when i = 21) it will throw the exception "It's out of range"
- in the other calls it will throw the exception "It's divisible by" for non-prime numbers only

Hope this helps.