In this case the decimal needs moved three places to the right.
26/21=1.238095...
1000*26/21=1238.095...
x = (1000*26/21)//1000
x=238

You could have
Code:
y=26
x = (1000*y/21)//1000
The above will only work if "y" is an integer 22 through 41.
When reading a sensor the range of values are fixed so with a little imagination a constant like in the above case 1000 will work. When another application comes along with a different set of values a different constant and equation will be required.

What is your application besides a keypad?