Thread: Help to Generalize my C Program.

My approach would be to have 3 variables minYear, mindMonth, minDay which would have the data of the earliest date as the user inputs again and again.
Example:
15/05/1992
15/02/2000
15/05/2012
0/0/0

• I read the first date. The earliest date is the 1st date.
• I read the 2nd date.Compare it with the min variables. If the 2nd date is earlier than the min variables, then assign the 2nd date to the min variables. Else, read next date.
• I read the third date.Compare it with the min variables. If the 3rd date is earlier than the min variables, then assign the 3rd date to the min variables. Else, read next date.
• I read 0/0/0. Print the min variables and exit.

I would use a do-while loop.

Also if you know structs, this application is ideal for them

It might help to first write a program which is basically the same but simpler -- write a program that asks the user for simple integers until the user enters the special integer -999. Afterwards, print the smallest integer that was entered. If you can make the program I just described, then you basically do the same thing for the date problem (except with the date you have three items to compare).

Also it might help if you have a compare function that works similarly to integers. For example, if you have integers x and y, then the following is how it is usually done:

Code:

if (x < y) {
   printf("x comes before y\n");
}else{
    printf("x does not come before y\n");
}

It is nice if we can basically do the same for a user defined type like a date. The conventional way is to make a comparison function which returns -1 if the first object is less than the second one, 0 if they are the same, and 1 if the first object is greater than the second object. The advantage is that the above integer test looks similar:

Code:

if (compare(mm_a, dd_a, yyyy_a, mm_b, dd_b, yyyy_b) < 0) {
    printf("Date a comes before date b\n");
}else{
    printf("Date a does not come before date b\n");
}

Why not using time.h library? I think it can save you a lot of work in programming and maintaining the code, and I'm pretty sure you can convert from one format to many formats using it.

Using ctime(), strptime() and tm structure can save you some time for this task.
more details regarding time.h can be found here

And if I posted here irrelevant information, I am terribly sorry.

Originally Posted by zeroice115

Why not using time.h library?

This is a good suggestion. The time.h defines a struct tm which includes members for years, months, days, etc. Then the functions you need are

strftime(3): format date/time - Linux man page (convert a struct tm into a string)
strptime(3) - Linux man page (convert a string into a struct tm)
mktime(3) - Linux man page (convert a struct tm into a time_t)
difftime(3): calculate time diff - Linux man page (compare two values of time_t)

Hmm... maybe the number of functions in time.h is intimidating for novice users. Maybe for learning purposes, design your own simple solution, and then come back to see how you can do something similar using the functions above.