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chapter 9 exercises
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‎ex.9.2.c

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// Calculate the number of days between two arbitrary dates
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#include <stdio.h>
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struct date
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{
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int month;
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int day;
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int year;
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};
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int yearInt (int year, int month)
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{
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if ( month <= 2 )
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return year - 1;
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else
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return year;
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}
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int monthInt (int month)
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{
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if ( month <= 2 )
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return month + 13;
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else
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return month + 1;
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}
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int dateInt (struct date d)
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{
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int yearN = 1461 * yearInt (d.year, d.month) / 4;
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int monthN = 153 * monthInt (d.month) / 5;
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return yearN + monthN + d.day;
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}
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int main (void)
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{
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struct date date1, date2;
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printf ("Type first date (mm dd yyyy): ");
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scanf ("%i %i %i", &date1.month, &date1.day, &date1.year);
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printf ("Type second date (mm dd yyyy): ");
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scanf ("%i %i %i", &date2.month, &date2.day, &date2.year);
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int n1 = dateInt (date1);
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int n2 = dateInt (date2);
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printf ("There are %i days between %i/%i/%.2i and %i/%i/%.2i\n", n2 - n1,
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date1.month, date1.day, date1.year % 100,
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date2.month, date2.day, date2.year % 100);
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return 0;
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}

‎ex.9.3.c

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// Calculate the elapsed time between two arbitrary times
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#include <stdio.h>
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struct time
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{
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int hour;
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int minutes;
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int seconds;
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};
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struct time elapsed_time (struct time t1, struct time t2)
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{
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int secondsDiff =
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(t2.hour * 3600 + t2.minutes * 60 + t2.seconds) -
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(t1.hour * 3600 + t1.minutes * 60 + t1.seconds);
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if ( secondsDiff < 0 )
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secondsDiff += 24 * 3600;
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struct time elapsed = {
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.hour = secondsDiff / 3600,
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.minutes = (secondsDiff % 3600) / 60,
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.seconds = (secondsDiff % 3600) % 60
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};
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return elapsed;
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}
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int main (void)
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{
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struct time time1, time2;
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printf ("Enter start time (hh:mm:ss): ");
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scanf ("%i:%i:%i", &time1.hour, &time1.minutes, &time1.seconds);
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printf ("Enter end time (hh:mm:ss): ");
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scanf ("%i:%i:%i", &time2.hour, &time2.minutes, &time2.seconds);
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struct time elapsed = elapsed_time (time1, time2);
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printf ("\nThe time elapsed between %.2i:%.2i:%.2i and %.2i:%.2i:%.2i",
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time1.hour, time1.minutes, time1.seconds,
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time2.hour, time2.minutes, time2.seconds);
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printf (" is %.2i:%.2i:%.2i\n",
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elapsed.hour, elapsed.minutes, elapsed.seconds);
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return 0;
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}

‎ex.9.4.c

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// Calculate the day of the week for an arbitrary date
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#include <stdio.h>
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struct date
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{
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int month;
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int day;
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int year;
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};
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int yearInt (int year, int month)
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{
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if ( month <= 2 )
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return year - 1;
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else
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return year;
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}
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int monthInt (int month)
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{
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if ( month <= 2 )
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return month + 13;
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else
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return month + 1;
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}
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int weekDayInt (struct date d)
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{
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int yearN = 1461 * yearInt (d.year, d.month) / 4;
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int monthN = 153 * monthInt (d.month) / 5;
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return (yearN + monthN + d.day - 621049) % 7;
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}
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int main (void)
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{
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const char weekDays[7][10] = {
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"Sunday", "Monday", "Tuesday", "Wednesday",
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"Thursday", "Friday", "Saturday"
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};
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struct date d;
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printf ("Which date (mm dd yyyy) do you want to know about? ");
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scanf ("%i %i %i", &d.month, &d.day, &d.year);
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int index = weekDayInt (d);
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printf ("%i/%i/%.2i falls on a %s\n",
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d.month, d.day, d.year % 100, weekDays[index]);
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return 0;
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}

‎ex.9.5.c

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// Program to update date and time
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#include <stdio.h>
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#include <stdbool.h>
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struct date
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{
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int month;
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int day;
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int year;
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};
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struct time
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{
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int hour;
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int minutes;
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int seconds;
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};
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struct dateAndTime
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{
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struct date sdate;
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struct time stime;
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};
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bool isMidnight (struct time t)
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{
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return t.hour == 0 && t.minutes == 0 && t.seconds == 0;
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}
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struct time timeUpdate (struct time t)
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{
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struct time updated = {
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.hour = t.hour, .minutes = t.minutes, .seconds = t.seconds + 1
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};
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if ( updated.seconds == 60 ) {
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updated.seconds = 0;
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updated.minutes += 1;
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if ( updated.minutes == 60 ) {
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updated.minutes = 0;
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updated.hour += 1;
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if ( updated.hour == 24 ) {
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updated.hour = 0;
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}
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}
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}
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return updated;
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}
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struct date dateUpdate (struct date today)
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{
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struct date tomorrow;
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int numberOfDays (struct date d);
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if ( today.day != numberOfDays (today) ) {
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tomorrow = (struct date) { today.month, today.day + 1, today.year };
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}
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else if ( today.month == 12 ) { // end of year
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tomorrow = (struct date) { 1, 1, today.year + 1 };
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}
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else { // end of month
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tomorrow = (struct date) { 1, today.month + 1, today.year };
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}
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return tomorrow;
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}
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// Function to find the number of days in a month
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int numberOfDays (struct date d)
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{
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int days;
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bool isLeapYear (struct date d);
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const int daysPerMonth[12] = {
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31, 28, 31, 30, 31, 30,
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31, 31, 30, 31, 30, 31
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};
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if ( isLeapYear (d) == true && d.month == 2 )
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days = 29;
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else
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days = daysPerMonth[d.month - 1];
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return days;
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}
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// Function to determine if it's a leap year
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bool isLeapYear (struct date d)
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{
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bool leapYearFlag;
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if ( (d.year % 4 == 0 && d.year % 100 != 0) || d.year % 400 == 0 )
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leapYearFlag = true; // It's a leap year
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else
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leapYearFlag = false; // Not a leap year
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return leapYearFlag;
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}
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struct dateAndTime clockKeeper (struct dateAndTime datetime)
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{
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struct dateAndTime updated = { .stime = timeUpdate (datetime.stime) };
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if ( isMidnight (updated.stime) )
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updated.sdate = dateUpdate (datetime.sdate);
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else
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updated.sdate = datetime.sdate;
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return updated;
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}
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int main (void)
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{
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struct dateAndTime datetime;
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printf ("Enter starting datetime (mm dd yyyy hh:mm:ss): ");
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scanf ("%i %i %i %i:%i:%i",
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&datetime.sdate.month, &datetime.sdate.day, &datetime.sdate.year,
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&datetime.stime.hour, &datetime.stime.minutes, &datetime.stime.seconds);
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struct dateAndTime updated = clockKeeper (datetime);
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printf ("\nThe updated datetime is %i/%i/%.2i %.2i:%.2i:%.2i\n",
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updated.sdate.month, updated.sdate.day, updated.sdate.year,
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updated.stime.hour, updated.stime.minutes, updated.stime.seconds);
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return 0;
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}

‎ex.9.6.c

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// Program to determine tomorrow's date
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#include <stdio.h>
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#include <stdbool.h>
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struct date
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{
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int month;
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int day;
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int year;
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};
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// Function to calculate tomorrow's date
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struct date dateUpdate (struct date today)
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{
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struct date tomorrow;
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int numberOfDays (struct date d);
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if ( today.day != numberOfDays (today) )
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tomorrow = (struct date) { today.month, today.day + 1, today.year };
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else if ( today.month == 12 ) // end of year
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tomorrow = (struct date) { 1, 1, today.year + 1 };
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else // end of month
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tomorrow = (struct date) { today.month + 1, 1, today.year };
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return tomorrow;
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}
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// Function to find the number of days in a month
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int numberOfDays (struct date d)
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{
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int days;
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bool isLeapYear (struct date d);
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const int daysPerMonth[12] = {
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31, 28, 31, 30, 31, 30,
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31, 31, 30, 31, 30, 31
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};
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if ( isLeapYear (d) == true && d.month == 2 )
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days = 29;
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else
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days = daysPerMonth[d.month - 1];
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return days;
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}
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// Function to determine if it's a leap year
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bool isLeapYear (struct date d)
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{
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bool leapYearFlag;
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if ( (d.year % 4 == 0 && d.year % 100 != 0) || d.year % 400 == 0 )
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leapYearFlag = true; // It's a leap year
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else
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leapYearFlag = false; // Not a leap year
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return leapYearFlag;
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}
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int main (void)
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{
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struct date dateUpdate (struct date today);
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struct date thisDay, nextDay;
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printf ("Enter today's date (mm dd yyyy): ");
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scanf ("%i%i%i", &thisDay.month, &thisDay.day, &thisDay.year);
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nextDay = dateUpdate (thisDay);
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printf ("Tomorrow's date is %i/%i/%.2i.\n", nextDay.month,
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nextDay.day, nextDay.year % 100);
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return 0;
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}

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