How do you write Hello world in dynamic C is this correct?

main()
{
printf("Hello World");
}

I'm not familiar with dynamic C, but assuming it's the Rabbit IDE, I'd recommend checking out the documentation here if you haven't already.

Assuming there is no initialisation required for printf then the code appears to be correct except that your main function should return an int:

int main(int argc, char **argp)
{
	printf("Hello World!");
	return 0;
}

Is there any specific issue you're having with the code like it not compiling or not giving the expected result?

Also, remember the code tags :)