Jonas Altrock ew20b126@technikum-wien.at

To overview.

The whole source file u5_calendar.c.

/* Compile with `clang -std=c99 -Wall -o u5_calendar u5_calendar.c` */
/* Test with `../checkproject u5_calendar` */

Include C-libraries for input/output.

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

Exercise 5: Loops: Calendar

Enter the number of days in a month and the day of week on the first of the month, then print a calendar of this month.

Details

Read two integer numbers. The first one is the numbers of the days of a month. The next one is the day-of-week of the first of the current month. 0 here is sunday which is also the day in the first column of the calendar. Print the calendar of this month where each row represents a week and all days in a column represent days on the same day of week. Each column should be 3 characters wide (use %3d to print the days for the correct format).

You may assume that only correct values are entered.

Example 1

Input:

31 0

Output:

 1  2  3  4  5  6  7
 8  9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31

Example 2

Input:

30 3

Output:

          1  2  3  4
 5  6  7  8  9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30
26 27 28 29 30

main()

int main() {

The user will input the number of days in the month, and the day of the week for the first day.

    int days, first;
    scanf("%d %d", &days, &first);

Loop through 0 to days + first, to get all ‘slots’ for days on the calendar.

    for (int i = 0; i < days + first; i++) {

Actual day in month: best understood by doing a concrete example, say i = 4, first = 3 (Wednesday), then day = 4 - 3 + 1 = 2, the second day of the month.

        int day = (i - first) + 1;

Before first real day, print empty column/slot, three spaces,

        if (day < 1) {
            printf("   ");
        }

else print the number with 3 characters, the prefix being the space character! 1 will be output as   1, 26 as  26.

        else {
            printf("% 3d", day);
        }

One row has a maximum of seven days (one week). i starts with 0, so we add 1 before using the modulo % operator to get the rest after dividing by 7.

That means i = 6 will print a line break.

        if ((i + 1) % 7 == 0) {
            printf("\n");
        }
    }

If our rows do not end at the last column, print an extra newline. Example:

• days = 30, first = 3
• days - (7 - first) == 30 - (7 - 3) == 26
• 26 % 7 == 5 The last day in the calendar will be two columns before the last one, meaning a Thursday.

    if ((days - (7 - first)) % 7 != 0) {
        printf("\n");
    }

Return code 0 for everything OK.

    return 0;
}