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Computer Literacy On-Line: Learning Unit 12

1. See Glossary.

"Go south on 4th Street to Jefferson Street" is an example of a repetition control structure in which we are instructed to "go until" a stopping condition occurs. "If there's anyone in the booth..." is an example of a sequence control structure. Sequence control structures include the list of instructions, which must be followed in sequence to complete the task.

"otherwise, just keep going" might be an ambiguous statement. Also the instruction "When you reach the bookstore parking lot..." How do you know you've reached the bookstore parking lot?

• Until you reach Jefferson Street
• Proceed south on 4th Street
• Turn left on Jefferson Street
• Proceed on Jefferson Street
• Until the booth at the campus entrance is reached,
• If booth has an attendant,
• Stop at booth
• Ask for permit to park in bookstore parking lot
• Else
• Continue on Jefferson Street
• When bookstore parking lot is reached
• Enter lot
• Until empty parking space is located,
• Circle the lot
• Park in empty spot.

• With HIGH=100 and LO=0
• While CHOICE is not the correct value
• Choose a value: CHOICE=(HIGH-LO)/2
• If CHOICE is too high,
• HIGH=CHOICE
• Else if CHOICE is too low
• LO=CHOICE

When the task you wish to perform is highly specialized and no off-the-shelf software exists that comes close to fitting the bill, it may be time to write custom software. Custom software is often far more expensive than off-the-shelf software, though, so it's important to explore all the possibilities before committing to a custom development effort.

Structured programming results in programs made up of logically cohesive modules that are arranged hierarchically. Structured programs are generally far easier to read, follow, and write than programs written using earlier techniques.

Computer programming languages are continuously being developed for different uses. Scientists have traditionally used different languages than business. Different computer users demand different types of computer languages, from the very low level to the very high level, and as new languages are introduced, the older languages continue in use.

An interpreter is a program that translates each statement of a program into machine language before passing it to the processor. A compiler translates an entire program into machine language before submitting it to the processor. An assembler is used to translate assembly language instructions into machine language.

Programmers use tools (programming languages) to develop software applications. Computer scientists develop the programming languages and methodologies for using those languages, to develop the best software possible.

Software errors can include errors of omission, syntax errors, logic errors, clerical errors, capacity errors, and judgment errors. Whatever the type of error, they can be extremely difficult to locate and correct, and can also create major malfunctions in the software causing user frustration or even company catastrophes.By improving programming techniques, programming environments, program verification, and human management, software engineers are continuously improving software reliability.