Multiply Table

#include <iostream>

using namespace std;

int main() {
    int num;
    cin >> num;

    for (int i = 1; i <= (num % 10); i++) {
        for (int j = 1; j <= ((num / 10) % 10); j++) {
            for (int k = 1; k <= (num / 100); k++) {
                cout << i << " * " << j << " * " << k << " = " << i * j * k << ";\n";
            }
        }
    }

    return 0;
}

Или:

#include <iostream>

using namespace std;

int main() {
    string num;
    cin >> num;

    for (int i = 1; i < num[0] - 47; i++) {
        for (int j = 1; j < num[1] - 47; j++) {
            for (int k = 1; k < num[2] - 47; k++) {
                cout << i << " * " << j << " * " << k << " = " << i * j * k << ";\n";
            }
        }
    }

    return 0;
}