Calendar not displaying correctly

[ajent047]

I am trying to get my calendar to display correctly for a project in my class. The calendar requires the user to input a number (1-12) for a month and a year no earlier than 1753. I think the problem(s) might reside in the computeOffset() and/or the displayCalendar() function(s). Here is the code:

#include <iostream>
#include <iomanip>
using namespace std;
int getMonth();
int getYear();
bool isLeapYear(int year);
int dayMonth(int month, int year);
int dayYear(int year);
int computeOffset(int month, int year);
void displayTop(int month, int year);
void displayCalendar(int offset, int daysMonth);
void display(int month, int year, int offset, int daysMonth);
/**********************************************************************
* This function will ask the user for a month and year, then display
* a calendar with the month and year above.
***********************************************************************/
int main()
{
int month = getMonth();
int year = getYear();
isLeapYear(year);
int daysMonth = dayMonth(month, year);
int daysYear = dayYear(year);
int offset = computeOffset(month, year);
display(month, year, offset, daysMonth);
return 0;
}

int getMonth()
{
int month;
cout << "Enter a month number: ";
cin >> month;
while (month < 1 || month > 12)
{
cout << "Month must be between 1 and 12.\n";
cout << "Enter a month number: ";
cin >> month;
}
return month;
}

int getYear()
{
int year;
cout << "Enter year: ";
cin >> year;
while (year < 1753)
{
cout << "Year must be 1753 or later.\n";
cout << "Enter year: ";
cin >> year;
}
return year;
}

bool isLeapYear(int year)
{
if (year % 4 == 0 && year % 100 != 0)
return true;
else if (year % 400 == 0)
return true;
else
return false;
}

int dayMonth(int month, int year)
{
int daysMonth;
if (month == 1 || month == 3 || month == 5 ||
month == 7 || month == 8 || month == 10 ||
month == 12)
daysMonth = 31;
else if (month == 4 || month == 6 ||
month == 9 || month == 11)
daysMonth = 30;
else if (month == 2)
{
bool isLeap = isLeapYear(year);
if (isLeap == true)
daysMonth = 29;
else
daysMonth = 28;
}
return daysMonth;
}

int dayYear(int year)
{
bool isLeap = isLeapYear(year);
int daysYear;
if (isLeap == true)
daysYear = 366;
else
daysYear = 365;
return daysYear;
}

int computeOffset(int month, int year)
{
int numDays = 0;
int numYears = year - 1753;
for (int yearCount = 1753; yearCount < year; yearCount++)
numDays += dayMonth(month, year);
for (int monthCount = 1; monthCount < month; monthCount++)
numDays += dayMonth(month, year);
int offset = numDays % 7;
return offset;
}

void displayTop(int month, int year)
{
cout << "\n";
if (month == 1)
cout << "January";
else if (month == 2)
cout << "February";
else if (month == 3)
cout << "March";
else if (month == 4)
cout << "April";
else if (month == 5)
cout << "May";
else if (month == 6)
cout << "June";
else if (month == 7)
cout << "July";
else if (month == 8)
cout << "August";
else if (month == 9)
cout << "September";
else if (month == 10)
cout << "October";
else if (month == 11)
cout << "November";
else if (month == 12)
cout << "December";
cout << ", " << year << "\n";
cout << " Su Mo Tu We Th Fr Sa\n";
}

void displayCalendar(int offset, int daysMonth)
{
int weekday;
int day;
if (offset == 0)
{
day = 2;
cout << setw(6);
}
else if (offset == 1)
{
day = 3;
cout << setw(10);
}
else if (offset == 2)
{
day = 4;
cout << setw(14);
}
else if (offset == 3)
{
day = 5;
cout << setw(18);
}
else if (offset == 4)
{
day = 6;
cout << setw(22);
}
else if (offset == 5)
{
day = 7;
cout << setw(26);
}
else if (offset == 6)
{
day = 1;
cout << setw(2);
}
for (weekday = 1; weekday <= daysMonth; weekday++)
{
cout << " " << setw(2) << weekday;
++day;
if (day == 8)
{
cout << "\n";
day = 1;
}
}
if (day >= 2 && day <= 7)
cout << "\n";
}

void display(int month, int year, int offset, int daysMonth)
{
displayTop(month, year);
int numDays = dayMonth(month, year);
displayCalendar(offset, daysMonth);
}

Most of the tests do not work. For example, the November 2002 calendar should start on Friday, but instead displays the following:

Enter a month number: 13
Month must be between 1 and 12.
Enter a month number: -1
Month must be between 1 and 12.
Enter a month number: 11
Enter year: 90
Year must be 1753 or later.
Enter year: -1
Year must be 1753 or later.
Enter year: 2002

November, 2002
Su Mo Tu We Th Fr Sa
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30

[Enoizat]

In main():
- you invoke isLeapYear() and then neglect its return value;
- you invoke dayYear() and save its return value into daysYear, and then you neglect it.

In computeOffset():
- you declare numYears and then you neglect it.

In display():
- you declare numDays and then you neglect it.

…[omissis]…

The compiler should have raised warnings for all these problem: I think you’d better not ignore what the compiler tells you!

Keep your code readable.
Sometimes switch is more legible than a sequence of if/else.
Don’t add an else if you don’t have to.

Please always surround your code by the code tags:
http://www.cplusplus.com/articles/jEywvCM9/
http://www.cplusplus.com/articles/z13hAqkS/


Just tidying your code up, the output improves (compared to your example):

#include <iostream>
#include <iomanip>


int getMonth();
int getYear();
bool isLeapYear(int year);
int dayMonth(int month, int year);
int dayYear(int year);
int computeOffset(int month, int year);
void displayTop(int month, int year);
void displayCalendar(int offset, int daysMonth);
void display(int month, int year, int offset, int daysMonth);


int main()
{
    int month = getMonth();
    int year = getYear();

    int daysMonth = dayMonth(month, year);

    int offset = computeOffset(month, year);

    display(month, year, offset, daysMonth);
    return 0;
}


int getMonth()
{
    std::cout << "Enter a month number: ";
    int month;
    std::cin >> month;
    while (month < 1 || 12 < month)
    {
        std::cout << "Month must be between 1 and 12.\nEnter a month number: ";
        std::cin >> month;
    }
    return month;
}


int getYear()
{
    std::cout << "Enter year: ";
    int year;
    std::cin >> year;
    while (year < 1753)
    {
        std::cout << "Year must be 1753 or later.\nEnter year: ";
        std::cin >> year;
    }
    return year;
}


bool isLeapYear(int year)
{
    if (year % 4 == 0 && year % 100 != 0) { return true; }
    if (year % 400 == 0)                  { return true; }
    return false;
}


// Returns -1 in case of error
int dayMonth(int month, int year)
{
    switch(month) {
    case 1: case 3: case 5: case 7: case 8: case 10: case 12:
        return 31;

    case 2:
        return isLeapYear(year) ? 29 : 28 ;

    case 4: case 6: case 9: case 11:
        return 30;

    default:
        return -1;
    }
}


int dayYear(int year)
{
    return isLeapYear(year) ? 366 : 365 ;
}


int computeOffset(int month, int year)
{
    int numDays = 0;
    // int numYears = year - 1753;

    for (int yearCount = 1753; yearCount < year; ++yearCount) {
        numDays += dayMonth(month, year);        
    }

    for (int monthCount = 1; monthCount < month; monthCount++) {
        numDays += dayMonth(month, year);
    }

    return numDays % 7;
}


void displayTop(int month, int year)
{
    std::cout << "\n";
    switch(month) {
    case  1: std::cout << "January";   break;
    case  2: std::cout << "February";  break;
    case  3: std::cout << "March";     break;
    case  4: std::cout << "April";     break;
    case  5: std::cout << "May";       break;
    case  6: std::cout << "June";      break;
    case  7: std::cout << "July";      break;
    case  8: std::cout << "August";    break;
    case  9: std::cout << "September"; break;
    case 10: std::cout << "October";   break;
    case 11: std::cout << "November";  break;
    case 12: std::cout << "December";  break;
    }
    std::cout << ", " << year << "\n";
    std::cout << " Su Mo Tu We Th Fr Sa\n";
}


void displayCalendar(int offset, int daysMonth)
{
    int weekday;
    int day;
    switch(offset) {
    case 0:
        day = 2;
        std::cout << std::setw(6);
        break;
    case 1:
        day = 3;
        std::cout << std::setw(10);
        break;
    case 2:
        day = 4;
        std::cout << std::setw(14);
        break;
    case 3:
        day = 5;
        std::cout << std::setw(18);
        break;
    case 4:
        day = 6;
        std::cout << std::setw(22);
        break;
    case 5:
        day = 7;
        std::cout << std::setw(26);
        break;
    case 6:
        day = 1;
        std::cout << std::setw(2);
        break;
    }

    for (weekday = 1; weekday <= daysMonth; ++weekday)
    {
        std::cout << ' ' << std::setw(2) << weekday;
        ++day;
        if (day == 8)
        {
            std::cout << "\n";
            day = 1;
        }
    }
    if (day >= 2 && day <= 7)
    std::cout << "\n";
}

void display(int month, int year, int offset, int daysMonth)
{
    displayTop(month, year);
    // int numDays = dayMonth(month, year);
    displayCalendar(offset, daysMonth);
}

Output:

Enter a month number: 11
Enter year: 2002

November, 2002
 Su Mo Tu We Th Fr Sa
       1  2  3  4  5  6
  7  8  9 10 11 12 13
 14 15 16 17 18 19 20
 21 22 23 24 25 26 27
 28 29 30

There are probably other issues I’m too lazy to look at :-/ but someone else’s likely to spot them.

[ajent047]

Unfortunately, this fails all of the tests because the offset is wrong. The 1st of November 2002 starts on Friday.