C++ Calendar (Cannot Get Value of Variable to Return to Main Function)

Question

Okay, so I have this project due for class by the 17th and I was wondering if I could get a bit of help. Basically, we are suppose to create a calendar that prints based on the day the Gregorian Calendar was created. I already figured out how to do the assignment but I am having trouble with leap year.

What I am having a problem with is returning the value of offset back to the main function so it can be used in another function. Perhaps this is a bit too advanced for my skills but I feel like this should be something fairly easy to do.

To give you an idea how leap year works. After the Century Offset does it's calculation, if the year is a leap year, it's suppose to subtract 1. Or in this case decrement. For some reason, the offset will not decrement for a leap year like 2016. If really confused as to why my if statement is not working. Can someone help?

//Write a program that will print a calendar for whatever year the user wants.

//Declaring libraries...some I might not need....
#include <iostream>
#include <cmath>
#include <iomanip>
#include <string>
#include <fstream>

using namespace std;

//Function prototypes
void ComputeCalendar(string [], string [], int, int);
void CenturyOffset(int year, int offset);
const int DAYS_OF_THE_WEEK = 7;
const int MONTHS_OF_THE_YEAR = 12;

//function calls

//Note: Use switch to calculate what day the calendar begins on

//Determines what day that calendar begins on
void CenturyOffset(int year, int offset){
    int c, y, z, s, d;

    c = year / 100;
    y = year % 100;
    z = y / 4;
    s = c + y + z;
    d = s % 7;
    offset = d;
    if (year % 4 == 0 && year % 400 == 0)
        offset--;
    cout << offset << endl;
    }

//function for creating the calendar
void ComputeCalendar(string months[], string days[], int year, int offset) {

    cout << "\n" << setw(50) << year << "\n" << endl;
    int cal;
    int week;
        for(cal=0; cal<MONTHS_OF_THE_YEAR; cal++)
            {
                cout << "\n" << endl;
                cout << setw(3) << months[cal] << " " << year << endl;
                cout << "\n" << endl;
                    for(week=0; week<DAYS_OF_THE_WEEK; week++)
                        {
                            cout << setw(5) << days[week];
                        }
                cout << endl;
            }
        }
//Main function that allows the user to input the year they wish to see
int main(int argc, char*argv[])
{
    int year;
    int offset;
    cout << "What year would you like to see the calendar for? \n" << endl;
    cin >> year;
    cout << "\n" << endl;

        while(year < 1754) //Check if the year was before or after 1754
            {
            cout << "You may not enter a year that is before 1754. \n" << endl;
            cout << "Please enter another year." << endl;
            cin >> year;
            cout << "\n" << endl;
            }
        string days[DAYS_OF_THE_WEEK] = {"SU","MO","TU","WE","TH","FR","SA"};             
//Stores days of the week in an array
        string months[MONTHS_OF_THE_YEAR] = {"January", "February", "March",
                                  "April", "May", "June",
                                  "July", "August", "September",
                                  "October", "November", "December"}; 
//Stores Months of the year in an array
        ComputeCalendar(months, days, year, offset);
        CenturyOffset(year, offset);
}

Answer 1

If you'd like to retain the value of offset when CenturyOffset(...) exits, change the function signature from:

void CenturyOffset(int year, int offset);

to

void CenturyOffset(int year, int& offset);

This way, offset is a reference .

Other links:

• Reference (C++)
• http://en.cppreference.com/w/cpp/language/reference

---

You may also return the value instead of having it passed as a parameter:

int CenturyOffset(int year) {
   int offset;
   // ...
   return offset
}

in main:

int offset = CenturyOffset(year);
// ...

Answer 2

Without modifying anything else, you can change your function signature to:

void CenturyOffset(int year, int& offset)

This passes a reference which will then modify the variable passed in from main , rather than a copy.

However, I would recommend changing the function to use a return:

int CenturyOffset(int year){
    int c, y, z, s, d, offset;

    c = year / 100;
    y = year % 100;
    z = y / 4;
    s = c + y + z;
    d = s % 7;
    offset = d;
    if (year % 4 == 0 && year % 400 == 0)
        offset--;
    return offset;
}

Now, you can get the value of offset in main :

int offset = CenturyOffset(year);
cout << offset << endl;
OtherFunction(offset);

Answer 3

Mainnote: Your Leap year logic is incorrect, it should be

year % 4 == 0 && year % 100 != 0 || year % 400 == 0

---

You have 2 options to return a value:

1) Use a return value

In this case You have to change the signature of your method:

int CenturyOffset( int year)

And in the body of this function You have to write:

return offset; 

Then in the body of your main function you use it as following:

int offset = CenturyOffset(year);

2) Return by reference (some people know it is an out value)

In this case You have to change the signature of your method:

void CenturyOffset( int year, int& offset)

And in the body of the function there is no change.

Then in the body of your main function you use it as following:

int offset = 0;                // always should initialize a value before use
CenturyOffset(year, offset);
...

Answer 4

Okay, so I solved this question by using the notes you guys gave me. I decided to use references in-order to get the integer back to the main function. I've acquired another problem however, I will post another question to solve this.

//Declaring Function prototypes int dayone(int year, int *offset, int *leapyear);

//Function calls

//This function determines what day the Calendar starts on int dayone(int year, int *offset, int *leapyear){ int c, y, z, s, d;

  c = year / 100;
  y = year % 100;
  z = y / 4;
  s = c + y + z;
  d = s % 7;
  *offset = d;
  *leapyear = 0;

    if(year % 4 == 0 || year % 400 == 0 && year % 100 != 0)
        {
            *offset--;
            *leapyear++;
        }
        return *offset, *leapyear;
      }
  //This is in int main(), didn't want to post the rest of the code since I've done a lot since then. 
 dayone(year, &offset, &leapyear);

That's what I came up with. I'm sorry if my question was a little confusing. Sometimes I have a hard time explaining what I want to do with a code.