4. Stores the results of manipulation in a specific location 5. Provides the user with an useful output Even with a simple program, such as the resistance program, each step must be broken down into a series of machine operations. These instructions, along with the parameters and data, must be translated into a language or code that the computer can understand. Programming is a complex problem that may involve writing a large number of instructions. It may also involve keeping track of a great many memory cells that are used for instruction and data storage, which is time-consuming and can lead to errors. To reduce time and the possibility of errors for complex program preparation, the compiler has been developed. The compiler is a program that takes certain commands and then writes, in a form the machine understands, the instructions necessary for a computer to execute these commands. Compilers can bring many instructions into the final program when called upon or signaled by a single source statement. The compiler is problem oriented because the operations produced are those needed to work the problem as set out by the problem statement. Compilers are built at various levels or degrees of complexity. The simplest form of compiler takes one mnemonic phrase and writes one machine instruction. A mnemonic code is an abbreviated term describing something to assist the human memory. For example, to shift the contents of the A-register right nine places, the mnemonic code RSH.A9 is used. This causes the compiler to write an instruction that shifts the contents of the A-register right 11₈ places. A compiler written on this level is commonly called an assembler. Note the advantages as follows: 1. No opportunity to use the wrong function code 2. No necessity to convert the shift count to octal A more sophisticated compiler may take a statement, such as “multiply principal by rate,” and generate all the instructions necessary for the computer to do the following: 1. Locate the factors involved (in this case the principal and rate) 2. Transfer these factors to the arithmetic unit 3. Perform the indicated arithmetic operation (in this case multiplication) 4. Store the resultant (which, in this case, will be the interest or the principal) The compiler also keeps track of all memory allocations, whether being used for data or instructions. Depending on the complexity of the problem to be solved, programs may vary in length from a few instructions to many thousands of instructions. Ultimately, the program could occupy a significant, perhaps even an excessive, portion of computer memory. One method used to preclude this possibility is to segment the program, storing seldom used portions in auxiliary storage, and reading these portions into the main memory only when they are required. An important method of developing this ability is through the use of subroutines. SUBROUTINES As a program grows larger, certain functions must be repeated. The instructions necessary to perform each of these repeated functions are grouped together to form subroutines. These subroutines may then be referenced by a relatively few instructions in the main program. This eliminates repeating certain groups of instructions throughout the program. EXECUTIVE ROUTINES The instructions that control access to the various subroutines are called the executive routine of the main program. Depending upon the complexity of the program, there may also be subexecutive routines within the executive routines. Housekeeping is a term used frequently with subroutines. At the time of entry into a subroutine, the contents of the various addressable registers may or may not be of value.    An addressable register is defined as any register whose contents can be altered under program control.    The programmer must take steps to preserve the contents of these registers unless they are of no value. JUMP AND RETURN JUMP INSTRUCTIONS The jump and return jump instructions are used to assist in the construction of executive routines. These instructions provide the computer with the ability to leave the sequential execution of the main program, execute any of the subroutines, and then return to the main program. 8-14