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[Ivan Kazmenko via Digitalmars-d-learn]

On Sunday, 21 February 2016 at 12:35:31 UTC, Lisa wrote:
> ...
> Is there smth wrong again?

Yes.

As a programmer, most of the time, you will have to try your 
programs by yourself before you consider them correct.

Now, run a compiler, and it complains:
-----
main.d(20): Error: cannot return non-void from void function
-----

Line 20 of your program is "return 0;", and the void function in 
question is "void main() {...}".  So, you have to fix either of 
that: make main return int instead of void, or remove the return 
line.

After that, the program will finally compile.  But that's not the 
end, you have to try running it.
"Enter side A:"
shall we say,
"1"
and then it writes
"Enter side B:"
and fails:
-----
std.conv.ConvException at c:\Tools\dmd\windows\bin\..\..\src\phobos\std\conv.d(2729): no digits seen
----------------
0x0040666A in ...
-----

That's a whole lot of unfriendly error text on the screen, but 
the human-readable part is "no digits seen" when reading variable 
B.

Now, read the chapter of Ali's book again very carefully, or one 
of the posts here.  You may then notice that the space inside the 
quotes is important, and also learn why.

The bottom line: the task of writing a program is not finished 
until you can compile it, run it, give it at least a few example 
inputs, and it prints the right output for all these inputs.

Ivan Kazmenko.