03
Sun, Dec
0 New Articles

# Use Advanced C Function to Find Distance Between Cities

###### Typography
• Smaller Small Medium Big Bigger
• Default Helvetica Segoe Georgia Times

Bust out your old trig textbooks to write some great code.

As programmers, we're often challenged with unusual requests, and we have to find creative ways to solve the problem.

Here is one such challenge. Based on the client's legacy code, we need to calculate mileage between two cities. The legacy code has a file, but it's not always populated correctly.

The solution is easier than you think. Using ZIP code coordinates, we can figure out how many miles are between cities--as the crow flies. There are Web services out there to calculate driving miles, but that's another article.

The best way to conquer this challenge is to use the cosine advanced math function. (For more information on cosine, just Google it.)

We all know that regular RPGLE doesn't allow advanced math functions such as trigonometry, so we need to add the C functions library to our RPGLE programs. First, we need to find latitude and longitude for a specific city. I used a third-party file that had all U.S. cities' coordinates by ZIP code. To best visualize this, follow the code. The two cities' ZIP codes in this example are 45817 (Bluffton, Ohio) and 45365 (Sidney, Ohio). The miles between them are 43.07.

H DFTACTGRP(*NO) BNDDIR('QC2LE')

DLAT1             S              8  6 inz(40.882285)

DLAT2             S              8  6 inz(40.286524)

DLON1             S              8  6 inz(-83.911911)

DLON2             S              8  6 inz(-84.155059)

DX                S             10  2

DY                S             10  2

D Miles           S             12  2

DCosine           PR             8F   ExtProc('cos')

D Double                         8F   value

Include the C function library in your program QC2LE. For this example, I hard-coded some coordinates for you (I know it's bad, but it works in this example). You will want to use your own file or screen to pass to your program for more flexibility. Make a procedure called "cosine" with the external process called "cos." Yes, it needs to be lowercase. The return is an eight-position floating point field.

/free

X = 69.1 *(lat2 - lat1);

Y = 69.1 *(lon2 - lon1) * cosine(lat1/57.3);

MILES = %SQRT(x*x + y*y);

//(result is 43.07 for this example)

*in69 = *on;

*inlr = *on;

Return;

The radius of the earth is 69.1 kilometers. Multiply the difference of latitude 2 minus latitude 1 by 69.1. Do the same for longitude, but multiply by the cosine of latitude 1 divided by 57.3. (To convert latitude or longitude from decimal degrees to radians, divide the latitude and longitude values in this database by 180/pi, or approximately 57.29577951.) You could do this without the cosine, but I found the results were not very accurate.

Next, use the square root of X*X + Y*Y, and you get miles. (If you use Mapquest to check this, it will likely show more miles from city to city. Again, this is because this example calculates distance as the crow flies, so there are no roads to consider.) To make this code more efficient, get a third-party file or use a Web service to get coordinates. There are lots of free Web services and files out there. Then just pass parameters to the program and return the miles.

This concludes today's tip. Using the C function on RPG adds lots to the functionality of RPGLE. There are many other C function APIs you can use as well. Most of them are more advanced and require a little more research. So dust off your old trig textbooks and start coding. I hope this was helpful to at least a few coders. Stay tuned for more tips like this in the future.

\$0.00 Raised:
\$

### Resource Center

• Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application. You can find Part 1 here. In Part 2 of our free Node.js Webinar Series, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Brian will briefly discuss the different tools available, and demonstrate his preferred setup for Node development on IBM i or any platform. Attend this webinar to learn:

• More than ever, there is a demand for IT to deliver innovation. Your IBM i has been an essential part of your business operations for years. However, your organization may struggle to maintain the current system and implement new projects. The thousands of customers we've worked with and surveyed state that expectations regarding the digital footprint and vision of the company are not aligned with the current IT environment.

• IBM announced the E1080 servers using the latest Power10 processor in September 2021. The most powerful processor from IBM to date, Power10 is designed to handle the demands of doing business in today’s high-tech atmosphere, including running cloud applications, supporting big data, and managing AI workloads. But what does Power10 mean for your data center? In this recorded webinar, IBMers Dan Sundt and Dylan Boday join IBM Power Champion Tom Huntington for a discussion on why Power10 technology is the right strategic investment if you run IBM i, AIX, or Linux. In this action-packed hour, Tom will share trends from the IBM i and AIX user communities while Dan and Dylan dive into the tech specs for key hardware, including:

• TRY the one package that solves all your document design and printing challenges on all your platforms. Produce bar code labels, electronic forms, ad hoc reports, and RFID tags – without programming! MarkMagic is the only document design and print solution that combines report writing, WYSIWYG label and forms design, and conditional printing in one integrated product. Make sure your data survives when catastrophe hits. Request your trial now!  Request Now.

• Forms of ransomware has been around for over 30 years, and with more and more organizations suffering attacks each year, it continues to endure. What has made ransomware such a durable threat and what is the best way to combat it? In order to prevent ransomware, organizations must first understand how it works.

• IT security is a top priority for businesses around the world, but most IBM i pros don’t know where to begin—and most cybersecurity experts don’t know IBM i. In this session, Robin Tatam explores the business impact of lax IBM i security, the top vulnerabilities putting IBM i at risk, and the steps you can take to protect your organization. If you’re looking to avoid unexpected downtime or corrupted data, you don’t want to miss this session.

• Can you trust all of your users all of the time? A typical end user receives 16 malicious emails each month, but only 17 percent of these phishing campaigns are reported to IT. Once an attack is underway, most organizations won’t discover the breach until six months later. A staggering amount of damage can occur in that time. Despite these risks, 93 percent of organizations are leaving their IBM i systems vulnerable to cybercrime. In this on-demand webinar, IBM i security experts Robin Tatam and Sandi Moore will reveal:

• Disaster protection is vital to every business. Yet, it often consists of patched together procedures that are prone to error. From automatic backups to data encryption to media management, Robot automates the routine (yet often complex) tasks of iSeries backup and recovery, saving you time and money and making the process safer and more reliable. Automate your backups with the Robot Backup and Recovery Solution. Key features include:

• Managing messages on your IBM i can be more than a full-time job if you have to do it manually. Messages need a response and resources must be monitored—often over multiple systems and across platforms. How can you be sure you won’t miss important system events? Automate your message center with the Robot Message Management Solution. Key features include:

• The thought of printing, distributing, and storing iSeries reports manually may reduce you to tears. Paper and labor costs associated with report generation can spiral out of control. Mountains of paper threaten to swamp your files. Robot automates report bursting, distribution, bundling, and archiving, and offers secure, selective online report viewing. Manage your reports with the Robot Report Management Solution. Key features include:

• For over 30 years, Robot has been a leader in systems management for IBM i. With batch job creation and scheduling at its core, the Robot Job Scheduling Solution reduces the opportunity for human error and helps you maintain service levels, automating even the biggest, most complex runbooks. Manage your job schedule with the Robot Job Scheduling Solution. Key features include:

• Business users want new applications now. Market and regulatory pressures require faster application updates and delivery into production. Your IBM i developers may be approaching retirement, and you see no sure way to fill their positions with experienced developers. In addition, you may be caught between maintaining your existing applications and the uncertainty of moving to something new.

• When it comes to creating your business applications, there are hundreds of coding platforms and programming languages to choose from. These options range from very complex traditional programming languages to Low-Code platforms where sometimes no traditional coding experience is needed. Download our whitepaper, The Power of Writing Code in a Low-Code Solution, and:

• Supply Chain is becoming increasingly complex and unpredictable. From raw materials for manufacturing to food supply chains, the journey from source to production to delivery to consumers is marred with inefficiencies, manual processes, shortages, recalls, counterfeits, and scandals. In this webinar, we discuss how:

• The MC Resource Centers bring you the widest selection of white papers, trial software, and on-demand webcasts for you to choose from. >> Review the list of White Papers, Trial Software or On-Demand Webcast at the MC Press Resource Center. >> Add the items to yru Cart and complet he checkout process and submit

• Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application.