int procedural_factorial(int n)
{
int fact = 1;
while (n > 1)
{
fact *= n;
n–;
}

return fact;
}

Here is another implementation of factorial written in a functional style:

int functional_factorial(const int n)
{
if (n <= 1)
{
return 1;
}
else
{
return n * functional_factorial(n-1);
}
}

Notice that the in the functional style the value of a variable is *never* mutated. In functional programming you don't mutate variables (all variables could be declared as constants) you just create new variables with new values. Also notice that the functional style uses recursion. Recursion is scary for C/C++ programmers because you're always worried about blowing your stack, in functional programming languages you can write recursive functions that don't grow the stack. At first glance it seems impossible to write any "real" programs if you're not allowed to mutate variables, but you can. You just have to develop a new way of thinking and solving problems.