Calendar Program

[tgarrisoniv]

task is to create a program that asks for year and prints calendar for entire year. this is by the far the largest program i have written so far. i am trying to take it in small pieces. i think the first step is to create a functioning calendar month and then a year and then inserting formulas for leap year and finding first day of the year. and then ridding of bugs. so far, i have written program for a calendar month but cannot get it to compile. it says that 'for' initial loop is only allowed in C99 mode and im not sure what that is. any idea?

#include <stdio.h>
#include <stdlib.h>


// Prototype Declarations
void printMonth (int startDay, int days);


int main(void)
{
// Statements
    printMonth (2,29);
    return 0;
}


void printMonth (int startDay, int days)
{


//Local Declarations
    int weekDay;


//Statements
    //print day header
    printf("Sun Mon Tue Wed Thu Fri Sat\n");
    printf("--- --- --- --- --- --- ---\n");


    //position first day
    for (weekDay = 0; weekDay < startDay; weekDay++)
        printf("    ");




    for (int dayCount = 1; dayCount <= days; dayCount++)
        {
        if (weekDay > 6)
            {
            printf("\n");
            weekDay = 1;
            } //if
        else
            weekDay++;
        printf("%3d ", dayCount);
        } //for
    printf("\n--- --- --- --- --- --- ---\n");
    return;
} // printMonth

error is for this line:

for (int dayCount = 1; dayCount <= days; dayCount++)

[memcpy]

That means you either have to declare the int outside the loop:

int dayCount;
for (dayCount = 1; dayCount <= days; dayCount++)

or compile as c99:

gcc -std=c99 main.c

Edit: this is because declaring variables inside the initialisation section of a for loop was illegal before C99 standard.

[javaeyes]

I did something like this years ago. Here's a tip. Calendars cycle every 28 years. This is because every year they are off by one day. If there were no leap years then it would cycle every 7 years. But with leap years its 28 years. So march 4th 2012 is sunday, and so march 4th 2040 will also be a sunday. Good luck.

[oogabooga]

Calendars cycle every 28 years. This is because every year they are off by one day. If there were no leap years then it would cycle every 7 years. But with leap years its 28 years.

Every 28 years must be something of a simplification since leap years are not EVERY 4 years. Leap years are every 4 years, except every 100 years, except every 400 years. I.e.:

int leapYear = (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;

[tgarrisoniv]

how do i make this repeat? my way is not working...

#include<stdio.h>
#include<stdlib.h>


// Global Declarations
int MonthDays[]={0,31,28,31,30,31,30,31,31,30,31,30,31};
char *months[]=
{
	" ",
	"\n\n\nJanuary",
	"\n\n\nFebruary",
	"\n\n\nMarch",
	"\n\n\nApril",
	"\n\n\nMay",
	"\n\n\nJune",
	"\n\n\nJuly",
	"\n\n\nAugust",
	"\n\n\nSeptember",
	"\n\n\nOctober",
	"\n\n\nNovember",
	"\n\n\nDecember"
};


int yearUsed(void)
{
	int year;


	printf("Please enter a year : ");
	scanf("%d", &year);
	return year;
}


int firstDay(int year)
{
	int findDay;
	int a;
	int b;
	int c;


	a = (year - 1.)/ 4.0;
	b = (year - 1.)/ 100.;
	c = (year - 1.)/ 400.;
	findDay = (year + a - b + c) %7;
	return findDay;
}


int Leapyear(int year)
{
	if(year% 4 == 0 && year%100 != 0 || year%400 == 0)
	{
    MonthDays[2] = 29;
    return 1;
	}
	else
	{
    MonthDays[2] = 28;
    return 0;
	}
}


void calendar(int year, int findDay)
{
	int month, day;
	for ( month = 1; month <= 12; month++ )
	{
    printf("%s %d", months[month], year);
    printf("\n\nSun  Mon  Tue  Wed  Thu  Fri  Sat\n" );


    // First Day
    for ( day = 1; day <= 1 + findDay * 5; day++ )
    {
        printf(" ");
    }


    // Print Month
    for ( day = 1; day <= MonthDays[month]; day++ )
    {
        printf("%2d", day );


    // If day before Sat or start Sun
    if ( ( day + findDay ) % 7 > 0 )
        printf("   " );
    else
        printf("\n " );
    }
    // Align month
    findDay = ( findDay + MonthDays[month] ) % 7;
	}
}


int main(void)
{
//Local Declarations
    char ans;
	int year, findDay, leapyear;


    do{


	year = yearUsed();
	findDay = firstDay(year);
	Leapyear(year);
	calendar(year, findDay);
	printf("\n");


    printf("y to continue\n");
    scanf("%s", ans);
}   while( ans[0] == 'y' || ans[0] == 'Y' );




} // Main

[nonoob]

I think it works OK. But I had to change ans to ans[10] so that it is an array since you check for ans[0].

[tgarrisoniv]

HMM.... doesnt work for me. it says subscribted value is neither array nor pointer for that line. i am running code blocks with gnuc compiler...

[tgarrisoniv]

ah i figured out my problem. works fine now. thanks for the tip!

[javaeyes]

Hmm didn't realize the 400 year leap year exception.