date_difference

#include<stdio.h>

int leap_year(int year);
//checks if a year is leap year or not

int days_in_month(int month_num);
//takes month number and returns number of days

int date_to_days(int date, int month, int year);
//takes date and calculate number of days from reference date

int days_to_date(int days);
//takes days and convert to date format

int main(){
    int year1, year2, month1, month2, date1, date2, result;
    printf("\nEnter valid date(dd mm yyyy)\nFirst date must be smaller than second date\n");
    printf("Enter first date: ");
    scanf("%d %d %d", &date1, &month1, &year1);
    printf("Enter second date: ");
    scanf("%d %d %d", &date2, &month2, &year2);
    if(date1>31 || date2>31 || month1>12 || month2>12){
        printf("Invalid date");
    }
    else{
        result = date_to_days(date2, month2, year2)-date_to_days(date1, month1, year1);
        printf("total number of days: %d\n", result);
        days_to_date(result);
    }
    return 0;
}

int leap_year(int year){
    if(((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0)){
        return 1;
    }
    else{
        return 0;
    }
}

int days_in_month(int month_num){
    int days=0, year=2018;
    if(month_num==1 ||month_num==3 ||month_num==5 ||month_num==7 ||month_num==8 ||month_num==10 ||month_num==12 ){
        return days+=31;
    }
    else if(month_num==4 ||month_num==6 ||month_num==9 ||month_num==11 ){
        return days+=30;
    }
    else if(month_num==2 && leap_year(year)){
        return days+=29;
    }
    else{
        return days+=28;
    }
}

int date_to_days(int date, int month, int year){
    int reference = 1500, result;
    int a=reference, b=(year-1), days=0;
    for(int i = a; i<=b; i++){
        if (leap_year(i)){
            days += 366;
        }
        else{
            days += 365;
        }
    }
    for(int i=1; i<=month; i++){
        days+=days_in_month(i);
    }
    days+=date;
    return days;

}

int days_to_date(int days){
    int year=0, month=0, date=0;
    if (days>=365){
        year = days/365;
        days-=year*365;
    }
    if (days>=30){
        month = days/30;
        days-=month*30;
    }
    printf("%d years, %d months, %d days", year, month, days);
    return 0;
}