You are checking whether a string contains a character literal of d (which lies in the range of characters between 0 to 9, both inclusive, in the ASCII table). Instead, you should convert d to an actual character or string representation for comparison.

I see, my bad.

Why is c++ not workin?

I thought you were doing C++ instead of C#.

Good. Did you changed languages at some point?

Please mark your post as having spoiler content next time. Your loop ends at the first number that doesn't contain a 5.

Read my answer to TechnoDiver just below ;)

Try to use braces systematically, your code will be more readable and this may be the cause of the error (and if it is not it will be easier to catch the problem).