Fortran

The simplest algorithm for calculating a difference between two times is to recast the times into a single, common axis, such as number of days since some point in the past. (Recall UNIX time from earlier in the chapter?) Once there, it’s straightforward to calculate the difference–it’s just a matter of subtracting one numerical value […]

We have our datetime and timedelta classes. The question remains: How can we take the difference between two datetimes using nothing but an arithmetic subtraction operator? Doing just td = birthday – now won’t work out of the box because a datetime is an arbitrary data structure. To the compiler, it has no intrinsic meaning and is just a sequence of numbers in memory. If we try this, we […]

Let’s first design a data structure to represent a time interval, or difference. How do we think of time intervals? They can be expressed as a number of days, hours, minutes, seconds, or any combination thereof. You may ask, Why not simply express the time difference as a finite number of days or seconds, like […]

Finally, we get to the meat of the countdown app: calculating the difference between the two times. There are three necessary ingredients for this to work: At the end of this section, we’ll be able to initialize two datetimes and take their difference, which should look something like this: ❶ Two datetime instances ❷ One timedelta instance […]

We got the date from the user input, and now we need to get the current date and time. Fortran provides a subroutine date_and_time that gives you access to the current local machine time. Here’s how it works, wrapped in a function to return a datetime instance: ❶ Array of eight integers ❷ Gets the date and time values and stores […]

There are a few different ways for a program to get input from the user. One is the so-called standard input, where the program waits for the user to enter data through the keyboard. This approach is useful when the program’s flow depends on users’ input. If you’re old enough to have grown up with […]

The simplest way to model human-readable date and time is by defining a data structure with integer components for each date and time unit. I say human-readable because most of us are quite used to thinking of dates in terms of years, months, and days, and times in terms of a 24-hour clock. A notable […]

In the first part of the implementation, we’ll define a datetime class and learn how to load it from command-line arguments and from local machine time.

From our specifications list, it looks like we’ll need some clever way to handle date and time data, as well as the time difference. In chapter 8, we learned how to define arbitrary data structures using derived types. We can thus model dates, times, and time difference structures as derived types (or classes)–let’s call these datetime and timedelta, […]

For the app to do well the one thing it’s supposed to do, it helps to set some specifications so we can plan the implementation: This specification list is plenty for this exercise. Now for the difficult part–how do we get this thing to work?