Expert: Joseph Moore - 10/6/2009

Question
QUESTION: Good day Sir.

I want to make a simple Daily Time Record system.  I need to know how to input the TIME-IN and TIME-OUT in this format, HH:MM and then get the total hours worked. Can you give me an example of this? Thank you very much for reading my letter. Best regards.

ANSWER: Hi, Josef.

The code below is one way to do this.  I don't know that it's the best way, but it is one way to do it and it is easy to implement.  It makes some assumptions and doesn't do a lot of error checking, but it works for simple input data.  In cases where the second time is less than the first time, it'll give weird results, I'm sure.  For a real time clock system, you would want a full time stamp with full date so that you can determine a true amount of time worked.  I've commented the relevant sections of code.  If you have any questions about this code, feel free to ask.

#include <iostream>
using namespace std;

bool parseTime(char* _timeStr, int& _hour, int& _min)
{
   // Make sure a pointer was passed in
   if (NULL == _timeStr)
       return false;

   // Hours starts at the string passed in, minutes we figure out in a second
   char* hourStr = _timeStr;
   char* minStr = NULL;

   // Loop through the string looking for the : character
   char* curChar = _timeStr;
   while (*curChar)
   {
       if (':' == *curChar)
       {
         // Found our minutes string. NULL terminate the hour string and set the minute string.
         *curChar = '\0';
         minStr = curChar + 1;
         break;
       }

       ++curChar;
   }

   // If no minute string was found, error
   if (NULL == minStr)
       return false;

   // Convert the strings to integers and store them
   _hour = atoi(hourStr);
   _min = atoi(minStr);

   // Restore the : character (could also use the "curChar" variable for this, but this way is more fun)
   *(minStr - 1) = ':';

   // Test for invalid values
   if (_hour < 0 || _hour > 23)
       return false;
   if (_min < 0 || _min > 59)
       return false;

   // Theoretical success!
   return true;
}

void main()
{
   char time1[80];
   char time2[80];

   cin >> time1;
   cin >> time2;

   int hour1, min1;
   int hour2, min2;

   if (!parseTime(time1, hour1, min1))
   {
       cout << "Error parsing time 1: " << time1 << ". Invalid time format.\n";
       exit(-1);
   }

   if (!parseTime(time2, hour2, min2))
   {
       cout << "Error parsing time 2: " << time2 << ". Invalid time format.\n";
       exit(-1);
   }

   // Hours worked and minutes worked
   int hoursWorked = hour2 - hour1;
   int minsWorked = min2 - min1;

   // It is possible that a full hour was not worked, meaning the minutes would be negative.
   if (minsWorked < 0)
   {
       // If that is the case, deduct one hour and add 60 minutes.  Since minutes is negative, this
       // yields the actual minutes worked (IE, -4 becomes 56).
       --hoursWorked;
       minsWorked += 60;
   }

   cout << "Time worked: " << hoursWorked << " hours, " << minsWorked << " minutes.\n";
}

---------- FOLLOW-UP ----------

QUESTION: Good day sir, here I am again. Just a follow up question sir. When I entered 08:00 for time-in and 17:01 for time-out, while replacing the last line of code with this one, cout<<hoursWorked<<":"<<minsWorked<<endl; it shows an output like this one; 9:1. How could I make this output like this, 09:01 instead of 9:1? I changed all int to float and the precision to 2 floating point but it still 9:1. Another thing is that, if I time-in on or before 08:00 and time-out on or after 17:00, it will still output an 8 hrs.

I hope you still answer my questions sir.  God bless you.

Sincerely,


Josef Alarka


Answer
Hi, Josef.

To format the numbers, you'll want to use printf:

   printf("Time worked -- %02d:%02d", hoursWorked, minsWorked);

The 02 before each d in the printf specify that it needs to be accurate to 2 digits and it will fill out 0's in the empty spots.

Also, I'm not entirely sure what you're asking with your last part.  Do you want it to limit to 8 hours and not display any hours over 8?  If that's the case, just add a couple of if blocks to the code after you calculate hoursWorked and minsWorked.  

Check first to see if hoursWorked is > 8, and limit it to 8 if it is greater.  Then, check if minsWorked is >= 8, and if it is, set minsWorked to 0.

Ok, hopefully that clears it all up.  If you have any further questions, don't hesitate to ask.