Sequential Control
Sequential control refers to the execution of statements in the order in which they were written by the programmer. Typically, sequential execution occurs in subroutines that, when combined, form the complete program code. The sequential execution is important as the execution of one statement can depend on the execution of a preceding statement.
In most programs, the sequential control is the default function. Unless otherwise commanded by the programmer, a computer will execute statements in stepwise order and will continue until a termination command is read. If a nonsequential order of statement execution is desired, this order must be written into the code by the programmer.
The use of a sequential control is especially beneficial in longer programs. In short programs, where only a few lines of code may be present, the execution of statements by the computer and the comprehension of the code by the programmer are easy. However, as the length of programming codes reaches thousands of lines, understanding the code becomes difficult. Breaking a program code into a series of blocks, which are called subroutines, helps alleviate confusion on the part of the programmer. The subroutines can be invoked, or called, as needed during the execution of the program. Within a subroutine, the execution of statements occurs sequentially. The final statement of a subroutine directs the computer to the next line of code. This step need not be sequential; the computer may not necessarily proceed sequentially, but can "jump" backwards or forwards to the next line of code. Put another way, sequential control permits an orderly and symmetrical function to be set up in a very non-symmetrical way. Sequential control flow of computation orders the computation process to save programming effort and time.
The use of sequential control within a subroutine can save programming time and the writing of code that is redundant. One of the advantages to the sequential control is that it allows an operation to be executed in a loop. If a subroutine can be invoked for various functions in a program, then the computer requires only to be guided to that subroutine. The same set of statements need not be re-written at various points in the code. The computer can be looped back to a subroutine and, because of sequential control within the subroutine, a common set of actions can be invoked. For functions that are required repeatedly in different applications, iterations followed by a programmed sequence of executable statements can save programming time and decrease programming error.
Sequential control has been used extensively in so-called concurrent programming languages, such as SR (Synchronizing Resources), Tempo, and Java. However, despite its benefits and applications, sequential controls have limitations. They are not well suited to the description of hardware, for example.
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