Java Reference
In-Depth Information
{
for (;timesByStart <= timesByEnd; timesByStart++)
{
document.write(timesTable + “ * “ + timesByStart + “ = “ +
timesByStart * timesTable + “<br />”);
}
}
var timesTable;
while ( (timesTable = prompt(“Enter the times table”,-1)) != -1)
{
while (isNaN(timesTable) == true)
{
timesTable = prompt(timesTable + “ is not a valid number, please retry”,-1);
}
if (timesTable == -1)
{
break;
}
document.write(“<br />The “ + timesTable + “ times table<br />”);
writeTimesTable(timesTable,1,12);
}
</script>
</body>
</html>
Save this as
ch3_q4.htm
.
The function remains the same, so let's look at the new code. The fi rst change from Question 3 is that
you declare a variable,
timesTable
, and then initialize it in the condition of the fi rst
while
loop. This
may seem like a strange thing to do at fi rst, but it does work. The code in parentheses inside the
while
loop's condition
(timesTable = prompt(“Enter the times table”,-1))
is executed fi rst because its order of precedence has been raised by the parentheses. This will return a
value, and it is this value that is compared to
-1
. If it's not
-1
, then the
while
condition is
true
, and the
body of the loop executes. Otherwise it's skipped over, and nothing else happens in this page.
In a second
while
loop nested inside the fi rst, you check to see that the value the user has entered is
actually a number using the function
isNaN()
. If it's not, then you prompt the user to try again, and
this will continue until a valid number is entered.
If the user had entered an invalid value initially, then in the second
while
loop, that user may have
entered
-1
, so following the
while
is an
if
statement that checks to see if
-1
has been entered. If it has,
you break out of the
while
loop; otherwise the
writeTimesTable()
function is called.
