The return value for main
indicates how the program exited. Normal exit is represented by a 0 return value from main
. Abnormal exit is signaled by a non-zero return, but there is no standard for how non-zero codes are interpreted. As noted by others, void main()
is prohibited by the C++ standard and should not be used. The valid C++ main
signatures are:
int main()
and
int main(int argc, char* argv[])
which is equivalent to
int main(int argc, char** argv)
It is also worth noting that in C++, int main()
can be left without a return-statement, at which point it defaults to returning 0. This is also true with a C99 program. Whether return 0;
should be omitted or not is open to debate. The range of valid C program main signatures is much greater.
Efficiency is not an issue with the main
function. It can only be entered and left once (marking the program's start and termination) according to the C++ standard. For C, re-entering main()
is allowed, but should be avoided.
Just about every modern operating system will recover all the allocated memory space after a program exits. The only exception I can think of might be something like Palm OS where the program's static storage and runtime memory are pretty much the same thing, so not freeing might cause the program to take up more storage. (I'm only speculating here.)
So generally, there's no harm in it, except the runtime cost of having more storage than you need. Certainly in the example you give, you want to keep the memory for a variable that might be used until it's cleared.
However, it's considered good style to free memory as soon as you don't need it any more, and to free anything you still have around on program exit. It's more of an exercise in knowing what memory you're using, and thinking about whether you still need it. If you don't keep track, you might have memory leaks.
On the other hand, the similar admonition to close your files on exit has a much more concrete result - if you don't, the data you wrote to them might not get flushed, or if they're a temp file, they might not get deleted when you're done. Also, database handles should have their transactions committed and then closed when you're done with them. Similarly, if you're using an object oriented language like C++ or Objective C, not freeing an object when you're done with it will mean the destructor will never get called, and any resources the class is responsible might not get cleaned up.
Best Solution
Well the
sleep()
function does it, there are several ways to use it;On linux:
And on windows you can use either dos.h or windows.h like this:
or you can use dos.h for linux style sleep like so:
And that is how you sleep in C on both windows and linux! For windows both methods should work. Just change the argument for # of seconds to what you need, and insert wherever you need a pause, like after the printf as I did. Also, Note: when using windows.h, please remember the capital
S
in sleep, and also thats its milliseconds! (Thanks to Chris for pointing that out)