It’s all come to this: Gathering up the individual functions necessary to code a program that outputs the current month, formatted, with the proper number of days for February. Coincidentally, this post is published in February.
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\nHere was my original request, from the January 4, 2014 lesson:<\/p>\n
I want the monthly calendar output to highlight the current day of the month.<\/p><\/blockquote>\n
The process I’ve shown over the past five weeks illustrates how a programmer would tackle such a problem:<\/p>\n
Phase I:<\/a> Figure out today’s date. You need that information primarily to obtain the current year and month, but also to help calculate the first day of the month.<\/p>\n
Phase II:<\/a> Determine on which day of the week is the first of the month. This calculation requires knowing the current day (Phase I), and it’s necessary when you want to format a calendar’s output.<\/p>\n
Phase III:<\/a> Once you have the first day of the month, the process of creating a calendar involves creating formatted output. The big issue then is knowing on which day of the month you stop displaying the calendar.<\/p>\n
Phase IV:<\/a> Next you have to deal with the February problem. Twenty five percent of the time February could be 29 days long instead of 28. That step involves creating a special days-of-the-month function.<\/p>\n
Phase V (this Lesson) brings it all together: The calendar output now contains a function to calculate the number of days in the month, including February. I also added one more element, which is to highlight the current day. That code is rather easy to implement: In the example below, an if<\/em> statement at Line 47 determines whether
day<\/code> (the day being output for the calendar) is equal tomday<\/code> (the current day of the month). If so, the printf()<\/em> function displays the date with square brackets around the number (Line 48).<\/p>\nHere’s the final code:<\/p>\n
\r\n#include <stdio.h>\r\n#include <time.h>\r\n\r\nint thefirst(int weekday, int monthday);\r\nint daysInMonth(int month,int year);\r\n\r\nint main()\r\n{\r\n time_t tictoc;\r\n struct tm *rightnow;\r\n int wday,mday,month,year,firstdom,dim,day,d;\r\n char *months[12] = {\r\n \"January\", \"February\", \"March\", \"April\",\r\n \"May\", \"June\", \"July\", \"August\",\r\n \"September\", \"October\", \"November\", \"December\" };\r\n\r\n time(&tictoc); \/* get Unix epoch time *\/\r\n \/* fill tm struct rightnow *\/\r\n rightnow = localtime(&tictoc);\r\n \/* Get info from struct *\/\r\n wday = rightnow->tm_wday; \/* 0=Sunday *\/\r\n mday = rightnow->tm_mday; \/* 1 to 31 *\/\r\n month = rightnow->tm_mon; \/* 0=January *\/\r\n year = rightnow->tm_year+1900; \/* current year - 1900 *\/\r\n\r\n\/* Display Calendar Header *\/\r\n printf(\"%s %d\\n\",months[month],year);\r\n printf(\"Sun Mon Tue Wed Thu Fri Sat\\n\");\r\n\r\n\/* Prep starting variables *\/\r\n firstdom = thefirst(wday,mday);\r\n dim = daysInMonth(month,year);\r\n day = 1; \/* Day of the month *\/\r\n\/* Display the days of the month *\/\r\n while( day <= dim )\r\n {\r\n for( d = 0; d < 7; d++)\r\n {\r\n \/* Test for the first week of the month *\/\r\n if( d < firstdom && day == 1 )\r\n {\r\n printf(\" \"); \/* blank date, 4 spaces *\/\r\n }\r\n else\r\n {\r\n \/* highlight current day *\/\r\n if( day == mday )\r\n printf(\"[%2d]\",day);\r\n else\r\n printf(\" %2d \",day);\r\n \/* check the next day *\/\r\n day++;\r\n if( day > dim )\r\n break;\r\n }\r\n }\r\n putchar('\\n');\r\n }\r\n\r\n return(0);\r\n}\r\n\r\n\/* Calculate First Day of the Month. *\/\r\nint thefirst(int weekday, int monthday)\r\n{\r\n int first;\r\n\r\n first = weekday - (monthday % 7) + 1;\r\n first %= 7;\r\n if( first < 0 )\r\n first+=7;\r\n\r\n return(first);\r\n}\r\n\r\n\/* Determine the number of days in the month *\/\r\nint daysInMonth(int month,int year)\r\n{\r\n int month_length[] = {\r\n 31, 28, 31, 30, 31, 30,\r\n 31, 31, 30, 31, 30, 31 };\r\n\r\n if(month != 1)\r\n return(month_length[month]);\r\n\r\n if( year % 4 )\r\n return(28);\r\n if( !(year % 100))\r\n {\r\n if( year % 400 )\r\n return(28);\r\n else\r\n return(29);\r\n }\r\n return(29);\r\n}<\/pre>\nHere’s the sample output (for today, February 1, 2014):<\/p>\n
February 2014\r\nSun Mon Tue Wed Thu Fri Sat\r\n [ 1]\r\n 2 3 4 5 6 7 8 \r\n 9 10 11 12 13 14 15 \r\n 16 17 18 19 20 21 22 \r\n 23 24 25 26 27 28 <\/code><\/pre>\nOne more addition you could make would be to center the month and year at the top of the calendar output. That involves a few tricks, but mostly pulling in your solution to January’s Exercise<\/a> on centering text.<\/p>\n","protected":false},"excerpt":{"rendered":"
The final in the Month Program series, here is the end result, a program that displays the current month and highlights the current day. Continue reading