Creating a Perpetual Calendar in C Language

Perpetual Calendar:Source Code:

#include <stdio.h>
#include <stdlib.h>
int year(int y){  // Determine if it's a leap year
    if ((y % 4 == 0) && (y % 100 != 0) || y % 400 == 0)
        return 366;  // Leap year
    else
        return 365;  // Common year
}

void printfStar()  // Custom function
{
    printf("*****************************\n");
}

int main(){
    int y;
    int i,j,sum = 0;
    int day ,week;
    int month[12] = {31,28,31,30,31,30,31,31,30,31,30,31};  // Days in each month for common year

    // Input the year for which the calendar is needed
    printf("Please enter the year:\n");
    scanf("%d",&y);
    if(year(y) == 366) month[1] = 29;  // Adjust February for leap year

    // Determine the day of the week for January 1st of the given year (Taylor's formula, January 1, 1900 is Monday)
    for(i = 1990; i < y; i++) sum += year(i);
    week = (sum + 1) % 7;
    printf("The calendar for %d is as follows:\n", y);
    for(i = 0; i < 12; i++){
        printf("\t %d month\n", i + 1);
        printf(" Sun Mon Tue Wed Thu Fri Sat\n");
        printfStar();  // Print star border

        // Calculate the day of the week for the first day of the month
        day = 1; // Start from the first day of a specific month
        for(j = 0; j < week; j++) printf(" ");
        while(day <= month[i]) // Days in each month
        {
            printf("%4d", day);  // Align the output
            day++;
            week = (week + 1) % 7;  // Calculate the day of the week

            // If a line reaches 7 numbers, move to the next line, corresponding to a week
            if(week % 7 == 0) printf("\n");  // New line
        }
        printf("\n"); // Space between months
        printfStar(); // Print star border
        printf("\n");
    }
    system("pause");  // Prevent console from closing
    return 0;
}

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