How do I find the next multiple of 10 of any integer?

Question

Dynamic integer will be any number from 0 to 150.

i.e. - number returns 41, need to return 50. If number is 10 need to return 10. Number is 1 need to return 10.

Was thinking I could use the ceiling function if I modify the integer as a decimal...? then use ceiling function, and put back to decimal?
Only thing is would also have to know if the number is 1, 2 or 3 digits (i.e. - 7 vs 94 vs 136)

Is there a better way to achieve this?

Thank You,

Answer 1

n + (10 - n % 10) 

How this works. The % operator evaluates to the remainder of the division (so 41 % 10 evaluates to 1, while 45 % 10 evaluates to 5). Subtracting that from 10 evaluates to how much how much you need to reach the next multiple.

The only issue is that this will turn 40 into 50. If you don't want that, you would need to add a check to make sure it's not already a multiple of 10.

if (n % 10)     n = n + (10 - n % 10); 

Answer 2

You can do this by performing integer division by 10 rounding up, and then multiplying the result by 10.

To divide A by B rounding up, add B - 1 to A and then divide it by B using "ordinary" integer division

Q = (A + B - 1) / B  

So, for your specific problem the while thing together will look as follows

A = (A + 9) / 10 * 10 

This will "snap" A to the next greater multiple of 10.

The need for the division and for the alignment comes up so often that normally in my programs I'd have macros for dividing [unsigned] integers with rounding up

#define UDIV_UP(a, b) (((a) + (b) - 1) / (b)) 

and for aligning an integer to the next boundary

#define ALIGN_UP(a, b) (UDIV_UP(a, b) * (b)) 

which would make the above look as

A = ALIGN_UP(A, 10); 

P.S. I don't know whether you need this extended to negative numbers. If you do, care should be taken to do it properly, depending on what you need as the result.