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Next: The mathematical function library
Up: Top-down design using Functions
Previous: Top-down design using Functions
A rationale for the use of functions has been given above. Basically
they save work in that having solved a problem once it need not be
solved again if there exists a function to solve the problem given the
particular parameters for this instance of the problem. In addition
the function can be comprehensively tested and hence a possible source
of error is eliminated in future programs. These reasons are now
expanded upon:
- When solving large problems it is usually necessary to split the
problem down into a series of sub-problems, which in turn may be split
into further sub-problems etc. This is usually called a
top-down approach. This process continues until problems
become of such a size that they can be solved by a single programmer.
This top-down approach is essential if the work has to be shared out
between a team of programmers, each programmer ending up with a
specification for a part of the system which is to be written as a
function (or functions). While writing a single function the
programmer is able to concentrate on the solution of this one problem
only and is thus more likely to be able to solve the problem and make
less errors. This function can now be tested on its own for
correctness.
- In a particular organisation or industry it may be found that in
carrying out the top-down approach in 1 some tasks occur very
frequently. For example the operation of sorting a file of data into
some order occurs frequently in data-processing applications. Thus a
library of such commonly used functions can be built up and
re-used in many different programs. This obviously saves much work
and cuts down errors if such functions have already been well tested.
- There are many very specialised problem areas, not every programmer
can know every area. For example many programmers working in
scientific applications will frequently use mathematical function
routines like sine and cosine, but would have no idea how to write
such routines. Similarly a programmer working in commercial
applications might know very little about how an efficient sorting
routine can be implemented. However a specialist can write such
routines, place them in a public library of functions and all
programmers can benefit from this expertise by being able to use these
efficient and well tested functions.
Before looking at how functions are implemented in C++ the use of the
mathematical function routines supplied in C++ is considered.
Next: The mathematical function library
Up: Top-down design using Functions
Previous: Top-down design using Functions
