Calendar Problem

I have to write a function which takes in a year between 1900 and 1999 and returns as a number the first day of that year. Days of the week go from 0 - 6 ( Sunday = 0, Saturday = 6).

I am supposed to use a leap year test to make this function work. I am also meant to make use of the fact that 1/1/1900 was a Monday. At the moment the program returns the correct value for the year 1900, but for every other year i enter i get "9" which is an invalid value. Any help??

Here is my code so far:

Code:

# include <stdio.h>

int new_years_day(int day, int year);
int no_of_days(int months, int year);
int first_day(int day, int year, int months);

int main(void)
{
	int choice, day = 0, months = 0, year = 0;
	printf("Choose a function\n (1) new_years_day (2) no_of_days (3) first_day >> ");
	scanf("%d", &choice);
	if (choice == 1)
		new_years_day(day, year);
		else if (choice == 2)
			no_of_days(months, year);
			else if (choice == 3)
				first_day(day, year, months);
				else 
				{
					printf("\nPlease enter a number between 1 and 3 >> ");
					scanf("%d", &choice);
				}
					return 0;
}


int new_years_day(int day, int year)
{
	int i = 0, leap = 0;

	// ask user for year between 1900 and 1999
	printf("Enter a year between 1900 and 1999 >> ");
	scanf("%d", &year);

	// check that user enters a valid year
	while (year < 1900 || year > 1999)
	{
		// print error message
		printf("You can only choose a year between 1900 and 1999!! >> ");
		scanf("%d", &year);
	}
	
	for ( i = day; day <= 6; day++)
	
	/* Problem: need to count no. of years after 1900 and loop between 0 and 6
	   the right number of times to get the right day */
	
	
	// leap year check

	while ((year % 400 == 0) && (year % 4 == 0) && (year % 100 > 0))	
			leap = 1;		// is a leap year
		
	// find correct day

		if (year == 1900)
		{
			day = 1;
			printf("\nThe first day of the year in %d was a %d (0 - Sunday, 6 - Saturday)\n", year, day);
		}
		else if (leap = 1)
		{
			day = day + 2;
			printf("\nThe first day of the year in %d was a %d (0 - Sunday, 6 - Saturday)\n", year, day);
		}
		else if (leap = 0)
		{
			day++;
			printf("\nThe first day of the year in %d was a %d (0 - Sunday, 6 - Saturday)\n", year, day);
		}
	
	return year, day;
}


int no_of_days(int months, int year)
{
	int i, current, leap = 0;

	// ask user for year between 1900 and 1999
	printf("Enter a year between 1900 and 1999 >> ");
	scanf("%d", &year);
	
	// check that user enters a valid year
	while (year < 1900 || year > 1999)
	{
		// print error message
		printf("You can only choose a year between 1900 and 1999!! >> ");
		scanf("%d", &year);
	}

	// ask user for a month between 1 and 12
	printf("Enter a month between 1 and 12 >> ");
	scanf("%d", &months);

	// check that user enters a valid month
	while (months < 1 || months > 12)
	{
		// print error message
		printf("You can only choose a month between 1 and 12!! >> ");
		scanf("%d", &months);
	}

	return months, year;
}


int first_day(int day, int year, int months)
{
	int i, current, leap = 0;

	// ask user for year between 1900 and 1999
	printf("Enter a year between 1900 and 1999 >> ");
	scanf("%d", &year);
	
	// check that user enters a valid year
	while (year < 1900 || year > 1999)
	{
		// print error message
		printf("You can only choose a year between 1900 and 1999!! >> ");
		scanf("%d", &year);
	}

	// ask user for a month between 1 and 12
	printf("Enter a month between 1 and 12 >> ");
	scanf("%d", &months);

	// check that user enters a valid month
	while (months <1 || months >12)
	{
		// print error message
		printf("You can only choose a month between 1 and 12!! >> ");
		scanf("%d", &months);
	}
	
	return day, year, months;
}

Firstly, you cannot return multiple values from functions. You only have one function that does something, namely new_years_day. The other two functions just accept user-input but they don't do anything.

Sorry bout the confusion but the other 2 functions are meant to be there cos i still have to build them yet. It's just that i'm stuck on the 1st function (new_years_day). Should I just have (return 0) at the bottom then instead of (return year, day), for example ??

Declare the function like this :
void new_years_day(int day, int year);

then you don't have to return anything.

Ok, thanks. So anybody got any ideas as to how i can make this function work then?

Code:

void new_years_day(int day, int year)
{
	int i = 0, leap = 0;

	// ask user for year between 1900 and 1999
	printf("Enter a year between 1900 and 1999 >> ");
	scanf("%d", &year);

	// check that user enters a valid year
	while (year < 1900 || year > 1999)
	{
		// print error message
		printf("You can only choose a year between 1900 and 1999!! >> ");
		scanf("%d", &year);
	}
	
	for ( i = day; day <= 6; day++)
	
	/* Problem: need to count no. of years after 1900 and loop between 0 and 6
	   the right number of times to get the right day */
	
	
	// leap year check

	while ((year % 400 == 0) && (year % 4 == 0) && (year % 100 > 0))	
			leap = 1;		// is a leap year
		
	// find correct day

		if (year == 1900)
		{
			day = 1;
			printf("\nThe first day of the year in %d was a %d (0 - Sunday, 6 - Saturday)\n", year, day);
		}
		else if (leap = 1)
		{
			day = day + 2;
			printf("\nThe first day of the year in %d was a %d (0 - Sunday, 6 - Saturday)\n", year, day);
		}
		else if (leap = 0)
		{
			day++;
			printf("\nThe first day of the year in %d was a %d (0 - Sunday, 6 - Saturday)\n", year, day);
		}
	
}

Please ??

Yeah, I've tried that but it makes very little difference. What I really need is a little help with the logic of how to actually code the solution. I know what I want to do, I just can't figure it out in terms of code or logical steps.

Cheers appreciate the help