Adding up total of mysql_num_rows in a while loop

Try something like this:

$Sum = 0;
while ($SomeInvariant)
{
   mysql_query($SomeQuery);
   $Sum += mysql_num_rows();
}

echo 'The sum is: ' . $Sum;

However, this approach is not very efficient (what if $SomeInvariant is true for many iterations, and your app has even more concurrent users?). To account for this, I would recommend restructuring your approach so the addition is done in SQL. This way, your query could look something like this: SELECT SUM(ColumnName) FROM ....

UPDATE: Addressing follow-up question in the comments

If you don't already have the sum available from the query, then you'll have to loop over the dataset twice. On the first pass, you'll calculate the sum. On the second pass, you'll calculate the ratio of each value to the sum.

For example:

$Sum = 0;
$Rows = array();
while ($SomeInvariant)
{
   mysql_query($SomeQuery);
   $Value = mysql_num_rows();
   $Rows[] = $Value; // Push the value onto the row array
   $Sum += $Value;   // Add the value to the cumulative sum
}

echo 'The sum is: ' . $Sum;

foreach ($Rows as $Row)
{
    echo $Row . '/' . $Sum . ' = ' . number_format($Row / $Sum) . '%';
}