Check out example codes for "what is difference between ciel and floor". It will help you in understanding the concepts better.

Code Example 1

Ceil (short for ceiling) and floor function are both mathematical 
functions. ... For example, ceil function returns the least value 
of the integer that is greater than or equal to the specified number.
On the other hand, floor function gets the greatest value that is
less than or equal to the specified number.

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