The simple answer is that you can't get percentages directly from csh. What you need is a scripting language that handles doubles or floats and most of the unix shell languages don't.
There is a special command line calculator (bc) that will work with floating values. It takes simple string commands and spits out the value. For example:
$ echo "40./57." | bc -l
.70175438596491228070
You can fake percentages in csh by using integers instead. Instead of dividing B by A, first multiply B by 100 and divide by A. The integer answer will be the percent value. If you want to have the answer rounded to the nearest percent, try RoundUp=(B*1000+A*5)/A*10.
If this is too painful, try a scripting language that supports doubles. Perl is one.