How to Write Programs

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Thankfully, the programmer does not have to worry about every electron and phosphor dot. He has enough on his hands typing his commands into the computer and testing them to see if they do what he meant them to do. Even a program for playing blackjack can quickly grow to be hundreds of lines long, each line densely packed with convoluted commands and alphanumerical characters. If there is even one character out of place in those hundreds of lines, chances are the program will not work properly. These software "bugs," as programming mishaps are called, can take weeks to find. One bug in an AT&T program knocked out all long-distance telephone service to Greece in 1979. It was months before Ma Bell's programmers pinned down the problem.

When the programmer has thoroughly tested and corrected his work he stores it on a magnetic tape,or disc, much as someone might use a tape recorder to store a noteworthy speech. A particularly useful or entertaining computer program might be accepted by one of the growing number of software publishers. They will copy the program onto blank discs and send them to computer stores around the country.

When a user slips his brand-new blackjack program into a disc drive and turns on his computer, the drive starts spinning the disc at a rate of hundreds of revolutions per minute. As the disc spins, a record-playback head moves across its surface, picking up the original programmer's typed instructions and loading them into the computer's memory. When the disc stops spinning—presto!—an exact replica of the program will be imprinted on the machine's temporary memory, all debugged and ready to deal the cards. Or, depending on the disc, proofread the term paper, balance the books or tell you to sell the hogs.

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