CS4ProgrammingWeek7

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Continue Khan Academy programming using Java Script https://www.khanacademy.org/cs


Monday


Tuesday

  • Peer review of Caesar Exploration programs.
  • Explore debugging program in Google Docs Script.

Caesar Cipher Google Script Workshop


Thursday (Lab)


Technology Friday

Test Test Test

Worlds First Fully Automated Plane Flown by a Computer...

Because this was the first fully fly-by-wire aircraft, the assumption was that this had to be a software bug. It turns out that the aircraft's systems all behaved correctly and the crash was a result of human error:

  • they were not experienced with the aircraft
  • flying too low and too slow
  • had no knowledge of the airfield
  • applied full power too late (takes time for engines to respond to power requests)

On a positive note - had this NOT been a computer controlled aircraft, there would have been nothing to stop the pilot from causing the craft to stall (insufficient airspeed for angle of attack), resulting in the craft dipping to the left or right. This would have caused the craft's crash to be more destructive.

As it happens, due to the software control, this A320 executed a perfect belly flop. 136 people were on board, three died.

Full details of the incident are here.


Ariane 5 Rocket Explodes

Software bug - tried to convert 64-bit floating point number to a 16-bit signed integer - conversion triggered an error (exception), resulting in a program crash.

16-Bit Integer

16-bit unsigned - range from 0 to 0xFFFF (65535) 16-bit signed - range from -32768 to +32767 (see here for more details)

64-Bit Floating Point Number
  • 64 Bits
    • Top 11 bits are exponent
    • Remaining 53 bits are fraction

(see here for more details)


Proton-M Explodes

Rocket's angular velocity sensors had been installed upside down.


Testing Summary

  • Software companies typically employ 1 dedicated software tester for every 3-6 software developers


Lab Continued