why we use function declaration and when we use it And why we don't use in the below example.

Question

main()
{
while(fun());
getch();
}
int fun()
{
static int x=4;
printf("%d",x);
return(--x);
}

Answer 1

The function "fun()" return type is int, so function declaration is not necessary.
As by default function returns integer. If a function returns other than integer it should be declared