Structured Programming (sometimes known as Modular Programming) is a subset of Procedural Programming that enforces a logical structure on the program being written to make it more efficient and easier to understand and modify.
Structured programming was first suggested by Corrado Bohm and Guiseppe Jacopini. The two mathematicians demonstrated that any computer program can be written with just three structures: Decisions, Sequences and Loops.
1) In "Decision" one of a number of statements is executed depending on the state of the program. This is usually expressed with keywords such as if..then..else..endif, switch, or case.
2) "Sequence" refers to an ordered execution of statements.
3) In "Loop" a statement is executed until the program reaches a certain state or operations are applied to every element of a collection. This is usually expressed with keywords such as while, repeat, for or do..until. Often it is recommended that each loop should only have one entry point (and in the original structural programming, also only one exit point), and a few languages enforce this.
Structured programming frequently (but not always) employs a top-down design model, in which developers map out the overall program structure into separate subsections. A defined function or set of similar functions is coded in a separate module or submodule, which means that code can be loaded into memory more efficiently and that modules can be reused in other programs. After a module has been tested individually, it is then integrated with other modules into the overall program structure.
It is possible to do structured programming in almost any procedural programming language, but since about 1970 when structured programming began to gain popularity as a technique, most new procedural programming languages have included features to encourage structured programming, (and sometimes have left out features that would make unstructured programming easy). Some of famous structured languages are ALGOL, PASCAL, Ada, C etc.
Coders should break larger pieces of code into shorter subroutines (functions and procedures in some languages) that are small enough to be understood easily. In general, programs should use global variables sparingly; instead, subroutines should use local variables and take arguments by either value or reference. These techniques help to make isolated small pieces of code easier to understand without having to understand the whole program at once.
Strictly speaking, in a structured programming language, any code structure should have only one entry point and one point of exit; many languages such as C allow multiple paths to a structure's exit (such as "continue", "break", and "return"), which can bring both advantages and disadvantages in readability.
So, Happy Programming.....
