Determining if a number is either a multiple of ten or within a particular set of ranges

Question

I have a few loops that I need in my program. I can write out the pseudo code, but I\'m not entirely sure how to write them logically.

I need -

if (num is          


        

Answer 1

The first one is easy. You just need to apply the modulo operator to your num value:

if ( ( num % 10 ) == 0)

Since C++ is evaluating every number that is not 0 as true, you could also write:

if ( ! ( num % 10 ) )  // Does not have a residue when divided by 10

For the second one, I think this is cleaner to understand:

The pattern repeats every 20, so you can calculate modulo 20. All elements you want will be in a row except the ones that are dividable by 20.

To get those too, just use num-1 or better num+19 to avoid dealing with negative numbers.

if ( ( ( num + 19 ) % 20 ) > 9 )

This is assuming the pattern repeats forever, so for 111-120 it would apply again, and so on. Otherwise you need to limit the numbers to 100:

if ( ( ( ( num + 19 ) % 20 ) > 9 ) && ( num <= 100 ) )