Say Digits

#include <iostream>
using namespace std;

void sayDigit(int n, string arr[]) {

    // Base case: if the number becomes 0, stop the recursion
    if(n == 0)
        return ;

    // Processing: Get the last digit of the number
    int digit = n % 10;
    n = n / 10;  // Remove the last digit from the number by integer division

    // Recursive call: Call the function with the remaining digits
    sayDigit(n, arr);

    // Output the word corresponding to the current digit
    cout << arr[digit] << " ";
}

Example Walkthrough:

string arr[10] = {"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine"};

Now, we call sayDigit(412, arr):

1. First recursive call:
   • n = 412
   • digit = 412 % 10 = 2
   • n = 412 / 10 = 41
   • Recursion calls sayDigit(41, arr).
2. Second recursive call:
   • n = 41
   • digit = 41 % 10 = 1
   • n = 41 / 10 = 4
   • Recursion calls sayDigit(4, arr).
3. Third recursive call:
   • n = 4
   • digit = 4 % 10 = 4
   • n = 4 / 10 = 0
   • Recursion calls sayDigit(0, arr) (base case).
4. The base case is hit (n == 0), so the recursion starts unwinding:
   • First, arr[4] = "four" is printed.
   • Then, arr[1] = "one" is printed.
   • Finally, arr[2] = "two" is printed.

Output:

four one two