Class 03 – Errors in Computing

Class 03 – Errors in Computing • Today’s Agenda • A short video about the Y2K issues in Hong Kong. • Classification and analysis of the error images collected. • Common ‘practices’ to create errors in software. • The biggest error in computing technology. • Errors used in digital art and music. • Glitch art. • Hands on exercises to go through the tactics of Jodi and Jim Punk.

Class 03 – Errors in Computing Y2K – the Hong Kong Connection I’ll go through the programming details afterward. You try to record the keywords that are often used to describe the issues, the impacts and the resolutions in the video.

Class 03 – Errors in Computing • Error sharing • Based on the material collected over the last two weeks, choose the 5 most interesting ones and describe them to us with the following in mind, • Who are the victims of the error? • What may be the causes of the error? • What did the users respond to the error? • What can be the impacts of the error? • Do you feel good with the error?

Class 03 – Errors in Computing Error handling Assumption: we do not want/like errors. But why?

Class 03 – Errors in Computing Error handling Errors cause troubles. Outage, blockage, interruption, etc. negative impacts. Impacts on productivity, security, stability.

Class 03 – Errors in Computing Mooninite http://edition.cnn.com/2007/US/02/01/boston.bombscare/index.html http://sweb.cityu.edu.hk/sm2263/class03/moon01.htm

Class 03 – Errors in Computing Error handling Scale / scope of the error Natural error – earthquake Mechanical failure – car engine breakdown Informational error – bug, programmed transaction Biological error – infection From local to global

Class 03 – Errors in Computing Error handling We somehow know we cannot completely eliminate errors. To err is human. We want to manage them. But how?

Class 03 – Errors in Computing Error handling Can we prevent the error? Can we avoid the error? Can we fix the error? Can we reduce the impact of the error?

Class 03 – Errors in Computing Error handling Our logic: for every error, there is a cause. When a machine is running smoothly for a period and suddenly there is an error, what will you think? Will you try to find out the cause of the error?

Class 03 – Errors in Computing Error handling Someone has changed something.

Class 03 – Errors in Computing Error recovery If we undo the change made by someone, can we resume the machine back to normal?

Class 03 – Errors in Computing Error resolution What if that someone makes the change again in the future? Can we not allow that someone to make any changes in the machine? Can we kill that someone? Can we modify the machine such that even if someone makes the change again, it won’t fail?

Class 03 – Errors in Computing Error preparation Can we try out the error situation such that we can prepare for the worst? Remember fire drill in primary school

Class 03 – Errors in Computing Benefits of errors Reveal exceptional situations. Reveal the deficiency of the initial design. Reveal a room for improvement. Reveal a lack of quality assurance. Reveal a spark of creativity?

Class 03 – Errors in Computing Common ‘practices’ to create errors in program Division by zero Mixing data type Rounding error Index out of bound Confusion with syntax Infinite loop File not found End of file Overwrite existing file

Class 03 – Errors in Computing Division by zero trace("division by zero"); var m:Number = 10; var n:Number = 0; trace(m/n);

Class 03 – Errors in Computing Mixed data type trace("invalid datatype"); var m:Number = 10; var n:Number = 7; var q:String = "12"; trace(m+n); trace(q+n);

Class 03 – Errors in Computing Round error The integer 3 will equal 3.3 if the later is rounded according to arithmetic function round(). There are cases where programmers purposely round down the dollar figures in bank accounts and transfer the cents into their own accounts which can be a significant sum.

Class 03 – Errors in Computing Index out of bound trace("array index error"); var m:Array = new Array(3); m[0] = 3; m[1] = 2; m[2] = 1; trace(m); trace(m.length); m[5] = 167; trace(m); trace(m.length);

Class 03 – Errors in Computing Confusion with syntax var m:Number = 0; var n:Number = 3; if (m=n) { trace("m = n"); } else { trace("m not = n"); }

Class 03 – Errors in Computing Infinite loop var i:Number = 1; var sum:Number = 0; while (i<100) { sum += i; }

Class 03 – Errors in Computing The biggest error in our times Y2k, the millennium bug Remember the coverage in media just before the year 2000.

Class 03 – Errors in Computing Y2K error var birth:Number = 87; var now:Number = 07; var age:Number = now - birth; trace(age);

Class 03 – Errors in Computing Y2K fix var birth:Number = 1987; var now:Number = 2007; var age:Number = now - birth; trace(age);

Class 03 – Errors in Computing Y2K fix var birth:Number = 83; var now:Number = 07; if (birth>50) { birth += 1900; } else { birth += 2000; } if (now>50) { now += 1900; } else { now += 2000; } var age:Number = now - birth; trace(age);

Class 03 – Errors in Computing Playing with the Y2K issue Y2K and the Millennium Butterflies

Class 03 – Errors in Computing Glitch arts A glitch is a short-lived fault in a system. The term is particularly common in the computing and electronics industries, as well as among players of video games, although it is applied to all types of systems including human organizations. From the German glitschen, meaning 'to slip.' from wikipedia

Class 03 – Errors in Computing • Glitch arts • Glitch as aesthetic that plays with errors and noise in the presentation of the artwork; • Glitch as a component of the creative process;

Class 03 – Errors in Computing Glitch music The use of digital artifacts, noise like distortion, which sound like digital errors in the process. Some artists physical scratch the medium, like pouring acid onto the cd surface to create glitch like sound.

Class 03 – Errors in Computing Glitch music Examples can be found in, Pan Sonic (formerly known as Panasonic) Kid606 Oval (Markus Popp) Autechre (Rob Brown, Sean Booth)

Class 03 – Errors in Computing Glitch music Pan Sonic

Class 03 – Errors in Computing Glitch music Kid606

Class 03 – Errors in Computing Glitch music Oval process

Class 03 – Errors in Computing Glitch music Autechre

Class 03 – Errors in Computing Glitch arts Tony Scott

Class 03 – Errors in Computing Glitch arts Tony Scott http://www.beflix.com

Class 03 – Errors in Computing Glitch arts Jason Salavon

Class 03 – Errors in Computing Glitch arts Alessandro Canova

Class 03 – Errors in Computing JavaScript exercises Understand scripting within a HTML page. Defining a function. Using some default events.

Class 03 – Errors in Computing JavaScript exercises <script language="Javascript"> function test01() { document.write("I love SM2263.<br>"); return; } test01(); </script>

Class 03 – Errors in Computing JavaScript exercises <script language="Javascript"> function test01() { document.write("I want to eat now.<br>"); return; } </script> <body onLoad="test01()">

Class 03 – Errors in Computing JavaScript exercises <script language="Javascript"> function test01() { window.resizeTo(100,100); window.moveTo(300,300); return; } </script> <body onLoad="test01()">

Class 03 – Errors in Computing JavaScript exercises <script language="JavaScript"> function test01() { window.status = "How are you?"; return; } </script> <body onLoad="test01()">

Class 03 – Errors in Computing JavaScript exercises <script language="JavaScript"> var i = 0; function test01() { i++; window.status = "counting to "+i; return; } function test02() { window.setInterval("test01()",1000); return; } test02(); </script>

Class 03 – Errors in Computing JavaScript exercises <script language="JavaScript"> var i = 0; function test01() { i++; document.myForm.myNum.value = i; return; } function test02() { window.setInterval("test01()",1000); return; } </script> <body onload="test02()">

Class 03 – Errors in Computing JavaScript exercises <script language="JavaScript"> function test01() { var x = screen.availWidth; var y = screen.availHeight; document.write("screen width is "+x+"<br>"); document.write("screen height is "+y+"<br>"); return; } test01(); </script>

Class 03 – Errors in Computing