Declaring variable in recursive function C++

Question

I wish to declare a variable w inside a recursive function. I have to declare it as f(a) (some function of a) where a is a parameter of the function. The problem is that the function is recursive and w changes value every time the recursive function is called (since a changes)

Is there a way to do keep w fixed to its first initialization?

#include <iostream>
using namespace std;

void foo(int a)
{ 
    if(a==1) return 0;
    // int w = f(a);
    //...some more lines of code that use 'w'
    // eg. return foo(a - 1);
}

Answer 1

The best way to implement a variable that keeps its state between function calls is to use the static keyword.

int AddOne_Static(void) {
    static int a;
    
    a++;
    
    return a;
}

int AddOne(void) {
    int a;
    
    a++;
    
    return a;
}

int main(void) {
    printf("%d\n", AddOne_Static());
    printf("%d\n", AddOne_Static());
    printf("%d\n", AddOne_Static());
    
    printf("%d\n", AddOne());
    printf("%d\n", AddOne());
    printf("%d\n", AddOne());
}

The Output will be:

1
2
3

1
1
1

This is a much cleaner way of declaring a variable that will keep its value between calls than a global which will also pollute the global namespace unnecessarily.

Answer 2

You could use a constant if you want to make 'w' a constant. Defining a constant may differ according to the language.

In your case, you cannot use w as a constant since the value of w is changed when the function gets recursive.

But if you need a constant which does not change its value over the runtime of the program, then, you definitely can define a constant globally or inside the function and use the value.

Hope you got your answer. :)