Create a formatted calendar

Question

I'm working on a project that creates a calendar based on user input of a month and a year. With that information, the code should count the number of days in that month and output a calendar. I would love to have extra eyes on my code. I'm still a beginner and limiting myself to just the libraries mentioned in the code!

I want to know if there is a simpler way to write this code or any suggestions on what I should change to make the code simpler. I was thinking of incorporating switch statements, but don't really know how to. Any feedback is appreciated! Right now my code looks oversimplified.. right?

#include <cmath>
#include <iostream>
using namespace std;

int month, day, year, start;

#define MONTHS_PER_YEAR 12 // Cannot change.

const unsigned short DAYS_PER_MONTH[MONTHS_PER_YEAR] =
    {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; // Cannot change.

const char MONTH_NAMES[MONTHS_PER_YEAR][10] =
    {"January",   "February", "March",    "April",
     "May",       "June",     "July",     "August",
     "September", "October",  "November", "December"}; // Cannot change.

bool leapYear()
{
    if (((year % 4 == 0) && year % 100 != 0) || year % 400 == 0)
    {
        return false;
    }
    else
    {
        return true;
    }
}
//I actually do not think I am supposed to use static.

int day_of()
{
    
    static int t[] = { 0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4 };
    year = year - month < 3;
    return ( year + year /4 - year /100 + year /400 + t[month-1] + day) % 7;
}

void printMonth()
{
    start = day_of();
    int count, days_in_month = DAYS_PER_MONTH[month - 1];
    if (leapYear() && month == 2)
    {
        days_in_month = DAYS_PER_MONTH[month - 1] + 1;
    }
    if (start == 6)
    {
        start = -1;
        cout << " ";
    } 
    for (count = 0; count <= start; count++)
    {
        cout << (count > 0? "   ": "    ");

    }
    for (day = 1; day <= days_in_month; day++)
    {
        if (++count > 6)
        {
            count = 0;
            if (day > 9)
            {
                cout << day << '\n';
            }
            else
            {
                cout << day << '\n' << " ";
            }
        }
        else
        {
            if (day >= 9)
            {
                cout << day;
            }
            else
            {
                cout << day << " ";
            }
            cout << " ";
        }
    }
    cout << endl;
}

// Controls operation of the program.
int main()
{
    cout << "Enter the month: ";
    cin >> month;
    cout << "Enter the year: ";
    cin >> year;
    cout << MONTH_NAMES[month - 1] << " " << year << std::endl;
    cout << "Su" << "  "<< "M" << "  "<< "T"<< "  " << "W" << " " << "Th" << "  " << "F" << " " << "Sa\n";
    printMonth();
    cout << endl;
    return 0;
}

Answer 1

That leapYear looks strange to me, to know if the year is leap year you need something like this:

bool leapYear()
{
    return !(((year % 4 == 0) && year % 100 != 0) || year % 400 == 0) ;
}

Some function name are a bit weird. Also what happens if somebody type month > 12?

#include <cmath>

is not necesary, since no math functions are used.

Answer 2

Don’t write using namespace std;.

int month, day, year, start; What's this doing here at the top of the file? Global variables, not even static, multiple on one statement, not initialized?

#define MONTHS_PER_YEAR 12 // Cannot change.

⧺ES.31 Don't use macros for constants or "functions"

I suggest you start by bookmarking the Standard Guidelines that I've linked to twice above, and browse through them to start getting familiar with them.

---

 if (something)
    {
        return false;
    }
    else
    {
        return true;
    }

In C++ (as in C), the something (the "condition") is not a special kind of syntax, but is just an expression like you use in arithmetic and anywhere else. You can have boolean variables and manipulate boolean values just like you do with numbers.

So, the grotesque formulation above is just what is meant by: return !something;

Right now my code looks oversimplified.. right?

On the contrary, it looks convoluted and overly wordy.

Thinking about when I wrote such a thing in 8-bit BASIC, I'd say you did a pretty good job of starting to organize it. You made several helper functions and defined constant data outside your main code. But once you got into that main logic, you micro-managed the whole process. printMonth is more if than actual logic.

You should have a simple call to print out a number in two characters, that always works whether it needs a leading space or not. That should not be inlined as more decisions to make inside printMonth itself! BTW, there are capabilities in the standard library for doing this.

Your printMonth should be simple and mostly list other functions to call. Continue to do "top-down decomposition" on the body of this function.