I need an explanation for this History question to help me study.
Unexpected input data makes your A-07 script “sum_from_x_to_y.php” produce wrong results.
In this age of computer viruses, trojan horses, spam, and a lot of other kinds of malicious attacks on servers, programs, and websites, it is a critical responsibility of any developer to program defensively. One must anticipate and proactively block ways in which any website or system could be compromised.
While your A-07 script has the basic functionality required in that assignment, it fails to prevent displaying misinformation or calculating some wrong results.
What did you miss? It is not what the spec said. (You got that part). It is what the spec did NOT say that you ignored or did not realize the developer must consider.
Your program likely produces the correct result in a narrow range of values, in particular for integers where the first integer is less than the second integer. If you are lucky in how you chose to set up your loop algorithm, your program might have the correct result when the first integer equals the second.
However, try at least these ordered value pairs (first, second) and look at the result of your program. Do you consider the result you are getting to be correct? You should also try other values of your choosing.
Assignment A-08 is to take your program from A-07 and make it “bulletproof”. If the user enters something improper for this program, give the user a clear message explaining the specific issue with what the user typed; then let the user correct it and run the corrected values.