Question

Use C++ to write a recursive function that takes in a non-negative integer and returns the count of the occurrences of 7 as a digit, so for example 717 yields 2. Note: Even though it would be easy to solve this problem iteratively, the goal is to get some practice solving problems recursively.

Answer 1

#include <iostream>

using namespace std;

int count7(int num) {
    if (num <= 0) {
        return 0;
    } else {
        int count = count7(num/10);
        if (num % 10 == 7) {
            count++;
        }
        return count;
    }
}

int main() {
    cout << count7(717) << endl;
    return 0;
}