They also insert comments in the coded instructions so other programmers can understand the program. Next, programmers test the operation of the program to be sure the instructions are correct and will produce the desired information. Programmers prepare sample data that will test every part of the program and review the results to see if any errors were made. If errors did occur, the program must be changed and rechecked until it produces the correct results. Finally, programmers prepare an instruction sheet for the computer operator who will run the program.
Programs vary with the type of problem to be solved.
For example, the arithmetical calculations involved in payroll accounting procedures are different from the mathematical calculations required to determine the flight path of the Space Shuttle. Although simple programs can be written in a few hours, programs that use complex mathematical formulas or many data files may require more than a year of work. In some cases, several programmers may work together in teams under a senior programmer's supervision. Applications programmers are usually oriented toward career, engineering or science. They write software to handle specific jobs, such as a program used in any inventory control system or one to control the temperature in an entire office building.