C++ for Scientists - Technische Universität Dresden

7.1. IMPERATIVE PROGRAMMING 201
7.1 Imperative Programming
Imperative programming may be viewed as the very bones on which all other abstractions
depend. This programming paradigm uses a sequence of instructions which act on a state to
realize algorithms. Thus it is always specified in detail what and how to execute next. The
modification of the program state while convenient is also an issue, as with increasing size of
the program, unintended modifications of the state becomes an increasing problem. In order
to address this issue the imperative programming method has been refined to procedural and
structured programming paradigms, which attempt to provide more control of the modifications
of the program state. Hence it is based upon organized procedure calls. Procedure calls, also
known as routines, subroutines, methods, or functions simply contain a series of computational
steps to be carried out. Any given procedure might be called at any point during a program’s
execution, including other procedures or itself. A function consists of:
• The return type of the function: A function returns the value at a user specified position.
C or C ++ which does not provide procedures explicitely has to use the keyword void for
indicating that a function does not return a value.
• The name of the function: Therewith the function can be called. The name should be as
expressive possible. Never underestimate names with good significance.
• The parameter list of the function: The parameters of a function serve as placeholders
for values that are later supplied by the user during each invocation of the function. A
function can have an empty parameter list. The values of the parameter list can be given
by value or by reference.
• The body of the function: The body of a function implements the logic of the operation.
Typically, it manipulates the named parameters of the function.
The advantages of this paradigm are:
• Few techniques
• Rapid prototyping for easy problems
• Functions can be put into a library
• Fast compilation
The disadvantages of this paradigm are:
• Test effort is high
• Source of error is manifold
• Non-trivial problems cause high programming line effort
• No user defined data types
• No locality of data
• Only very few and simple functions can be put into a library
Even in the refined form as procedural programming the incurred overhead can be limited to a
bare minimum as the level of abstraction is relatively low. This was well suited for the situation