sum_days_from_start_of_year

#include <stdio.h>

void main () {
    int inMonth;
    int inYear;
    int inDay;
    int daysPassedFromStartOfYear = 0;
    int currMonth;

    printf("Enter year: ");
    scanf("%d", &inYear);

    printf("Enter month: ");
    scanf("%d", &inMonth);

    printf("Enter day: ");
    scanf("%d", &inDay);

    // Sum days of all months before the current month
    for (currMonth = 1; currMonth < inMonth; currMonth++) {
        daysPassedFromStartOfYear += GetDaysInMonth(inYear, currMonth);
    }

    // Add days passed this month
    daysPassedFromStartOfYear += inDay;

    printf("Days passed: %d\n", daysPassedFromStartOfYear);
}

int GetDaysInMonth(int year, int month) {
    int days = 0;

    switch( month ) {
        case 1:
        case 3:
        case 5:
        case 7:
        case 8:
        case 10:
        case 12:
            days = 31;
            break;
        case 4:
        case 6:
        case 9:
        case 11:
            days = 30;
            break;
        case 2:
            if (year % 4 == 0)
                days = 29;
            else
                days = 28;
            break;
        default:
            days = 0;
            break;
    }

    return days;
}