Decrement Date

// ConsoleApplication3.cpp: определяет точку входа для консольного приложения.
//

#include "stdafx.h"
#include <stdio.h>
#include <iostream>

#define MAX_MONTH 12

int monthsMaxDays[] = {
    31, // JAN
    28, // FEB
    31, // ...
    30,
    31,
    30,
    31,
    31,
    30,
    31,
    30,
    31
};

void decDate(int &m, int &d);
bool validateInput(const int m, const int d);

int main()
{
    int d, m;
    std::cout << "Month: ";
    std::cin >> m;
    std::cout << "Day: ";
    std::cin >> d;

    if (!validateInput(m, d)) {
        return -1;
    }

    decDate(m, d);

    std::cout << "Previous date: Month = " << m << ", Day = " << d;

    return 0;
}

void decDate(int &m, int &d)
{
    d -= 1;

    if (d == 0) {
        d = monthsMaxDays[m - 2];

        m -= 1;

        if (m == 0) {
            m = MAX_MONTH;
        }
    }
}

bool validateInput(const int m, const int d) {
    if (m > MAX_MONTH || m <= 0) {
        std::cerr << "Month must be greater than 0 and lesser than 12";
        return false;
    }

    if (d > monthsMaxDays[m - 1] || m <= 0) {
        std::cerr << "Day must be greater than 0 and lesser its max value";
        return false;
    }

    return true;
}