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PODay month and year algorithm using Gettimeofday() in C
 

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  1. PODay month and year algorithm using Gettimeofday() in C
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    <p>Im required as part of a lab to devise a way to calculate the current month day and year. I'll be using the gettimeofday() function which gives me the number of seconds since january 1 1970.</p> <p>I know that there are functions that will do the conversoins for me, however the design requirement is that i create my own algorithm for converting the seconds to months days and years. The manner in which I want to implement my design is with a lookup table for each of the twelve months and the corresponding number of days. The logic is a little befuddling to me right now.</p> <p>The tricky part is handling the leap years. I know that 1972 is the first leap year since 1970. And a leap year occurs every 4 years since that date. The hint given to me in this assignment is that the next largest cycle after days is 4 years. So if I modulus the number of days since 1970 by 1461 (number of days in 4 years) I know I can get the number of days left over. Its at this point my train of logic gets lost. If I DIVIDE it by 1461 it just tells me the how many 4 year periods have gone by. </p> <p>The table I want to implement will look something like this ( i know the coding isnt completely right but just to show what im getting at):</p> <pre><code>struct Monthdays { int days; char* Monthname[] }; Monthdays lookupMonths[] { {31,"January"} {28,"February"} . . . }; </code></pre> <p>Im trying to figure out how to create a proper index using the number of days or something to walk through this "table".........I hope asking this here is okay. I've been struggling with the logic or a couple of days right now....</p> <p>Here is the code for this problem i have now which is very inefficient.</p> <pre><code> ExpandedTime* localTime( struct timeval* tv, // Pointer to timeval struct ExpandedTime* etime // '' '' to expandedtime strct ) { tzset(); // Corrects for timezone int epochT = (tv-&gt;tv_sec) - timezone; // Epoch seconds with int epochUT = tv-&gt;tv_usec; // epochtime microseconds int edays; // Days since epochtime etime-&gt;et_usec = (epochUT/milli) % milli; // Find the milliseconds etime-&gt;et_sec = epochT % 60; epochT /= 60; // Turn into minutes etime-&gt;et_min = epochT % 60; epochT /= 60; // Turn into hours if (localtime(&amp;tv-&gt;tv_sec)-&gt;tm_isdst !=0) etime-&gt;et_hour = (epochT % 24) + daylight; // Hours with DST correc else etime-&gt;et_hour = (epochT % 24); edays = epochT /= 24; // Turn into days etime-&gt;et_day = epochT; // Delete up to here etime-&gt;et_year = (epochT/365) + epochyear; // Get the current year int trackyear; // Counter for years int trackdays = -1; // Subtracting janurary 1st // from days // This will determine if it is a leapyear and adjust days accordingly // from 1970 to current year (2013) for (trackyear = epochyear; trackyear &lt; etime-&gt;et_year; trackyear++) { if (trackyear % leapy == 0) { trackdays = trackdays + 366; } else { trackdays = trackdays + 365; } } etime-&gt;et_day = edays - trackdays; int trackmonth = -1; // Counter for months // with offset to make // january = 0 // This will give me the number of months for the buffer do { switch (trackmonth) { // Months with 31 days case 0: etime-&gt;et_day = (etime-&gt;et_day) - 31; break; case 2: etime-&gt;et_day = (etime-&gt;et_day) - 31; break; case 4: etime-&gt;et_day = (etime-&gt;et_day) - 31; break; case 6: etime-&gt;et_day = (etime-&gt;et_day) - 31; break; case 7: etime-&gt;et_day = (etime-&gt;et_day) - 31; break; case 9: etime-&gt;et_day = (etime-&gt;et_day) - 31; break; case 11: etime-&gt;et_day = (etime-&gt;et_day) - 31; break; // Months with only 30 days case 3: etime-&gt;et_day = (etime-&gt;et_day) - 30; break; case 5: etime-&gt;et_day = (etime-&gt;et_day) - 30; break; case 8: etime-&gt;et_day = (etime-&gt;et_day) - 30; break; case 10: etime-&gt;et_day = (etime-&gt;et_day) - 30; break; // Leap year month a.k.a Febuary case 1: if (trackyear % leapy) { etime-&gt;et_day = (etime-&gt;et_day) - 28; } else { etime-&gt;et_day = (etime-&gt;et_day) - 29; } break; } trackmonth++; } while(etime-&gt;et_day &gt; 0); etime-&gt;et_mon = trackmonth - 1; // Reverts day offset from previous switch to // accurately represent the current day switch (etime-&gt;et_mon) { // Months with 31 days case 0: etime-&gt;et_day = (etime-&gt;et_day) + 31; break; case 2: etime-&gt;et_day = (etime-&gt;et_day) + 31; break; case 4: etime-&gt;et_day = (etime-&gt;et_day) + 31; break; case 6: etime-&gt;et_day = (etime-&gt;et_day) + 31; break; case 7: etime-&gt;et_day = (etime-&gt;et_day) + 31; break; case 9: etime-&gt;et_day = (etime-&gt;et_day) + 31; break; case 11: etime-&gt;et_day = (etime-&gt;et_day) + 31; break; // Months with only 30 days case 3: etime-&gt;et_day = (etime-&gt;et_day) + 30; break; case 5: etime-&gt;et_day = (etime-&gt;et_day) + 30; break; case 8: etime-&gt;et_day = (etime-&gt;et_day) + 30; break; case 10: etime-&gt;et_day = (etime-&gt;et_day) + 30; break; // Leap year month a.k.a Febuary case 1: if (trackyear % leapy) { etime-&gt;et_day = (etime-&gt;et_day) + 28; } else { etime-&gt;et_day = (etime-&gt;et_day) + 29; } break; } return etime; } </code></pre>
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    1. CO[spoiler](http://stackoverflow.com/a/11197532/968261). But look at the comments, how I arranged the years to cope with leap years.
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    2. COHi welcome, to Stackoverflow. This is a forum for getting help with programming and it is in poor taste to post something without attempting the problem. If you've given this a shot and can't figure out why it's not working post your code and you'll get much more help.
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    3. COI've tried the problem. I have a copy and paste method right now which is terribly inefficient. Its also 230 lines long (the program does other things as well) so I figured noone would want to read through all of that.
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