C++ source code to compute modular exponetiation recursively.

ModularExponentiation2.cpp

/***************************************************************
 * Modular Exponentiation (recursive).
 **************************************************************/
#include <iostream>
#include <stdlib.h>

using namespace std;

class ModularExponentiation
{
    int ans;                    // Answer
public:
    int compME(int, int, int);  // Compute Modular Exponentiation
};

/*
 * Compute Modular Exponentiation
 */
int ModularExponentiation::compME(int b, int e, int m)
{
    if (e == 0) return 1;

    ans = compME(b, e / 2, m);
    ans = (ans * ans) % m;
    if (e % 2 == 1) ans = (ans * b) % m;

    return ans;
}

int main()
{
    try
    {
        int b, e, m, me;  // me = b^e mod m
        b = 12345; e = 6789; m = 4567;

        // Instantiation
        ModularExponentiation objMain;

        // Compute Modular Exponentiation
        me = objMain.compME(b, e, m);

        // Display
        cout << b << "^" << e << " mod " << m << " = "
             << me << endl;
    }
    catch (...) {
        cout << "ERROR!" << endl;
        return EXIT_FAILURE;
    }

    return EXIT_SUCCESS;
}