Try input that increases See how the computer s answer changes when the input changes from 2 to 1000. If your program contains division, try input that will make the divisor be zero or a tiny decimal close to zero. If your program contains the square root of a quantity, try input that will make the quantity be negative. A computer can print a wrong answer because its circuitry is broken or because a program has a bug. But the main reason why computers print wrong answers is incorrect input .
Incorrect input is called garbage and has several causes.
The user s finger slips Instead of 400, he inputs 4000. Instead of 27, he inputs 72. Trying to type .753, he leaves out the decimal point. The user got wrong information He tries to input the temperature, but his thermometer is leaking. He tries to input the results of a questionnaire, but everybody who filled out his questionnaires lied.