Pseudo-code
Programmers have yet another form of programming language called
pseudo-code. Pseudo-code is simply English arranged with a general structure
similar to a high-level language. It isn’t understood by compilers, assemblers,
or any computers, but it is a useful way for a programmer to arrange instructions.
Pseudo-code isn’t well defined; in fact, most people write pseudo-code
slightly differently. It’s sort of the nebulous missing link between English and
high-level programming languages like C. Pseudo-code makes for an excellent
introduction to common universal programming concepts.
Control Structures
Without control structures, a program would just be a series of instructions
executed in sequential order. This is fine for very simple programs, but most
programs, like the driving directions example, aren’t that simple. The driving
directions included statements like, Continue on Main Street until you see a
church on your right and If the street is blocked because of construction.These
statements are known as control structures, and they change the flow of the
program’s execution from a simple sequential order to a more complex and
more useful flow.
Without control structures, a program would just be a series of instructions
executed in sequential order. This is fine for very simple programs, but most
programs, like the driving directions example, aren’t that simple. The driving
directions included statements like, Continue on Main Street until you see a
church on your right and If the street is blocked because of construction.These
statements are known as control structures, and they change the flow of the
program’s execution from a simple sequential order to a more complex and
more useful flow.
If-Then-Else
In the case of our driving directions, Main Street could be under construction.
If it is, a special set of instructions needs to address that situation. Otherwise,
the original set of instructions should be followed. These types of special cases
can be accounted for in a program with one of the most natural control
structures: the if-then-else structure. In general, it looks something like this:
If (condition) then
{
Set of instructions to execute if the condition is met;
}
Else
{
Set of instruction to execute if the condition is not met;
}
For this book, a C-like pseudo-code will be used, so every instruction will
end with a semicolon, and the sets of instructions will be grouped with curly
braces and indentation. The if-then-else pseudo-code structure of the preceding
driving directions might look something like this:
Drive down Main Street;
If (street is blocked)
{
Turn right on 15th Street;
Turn left on Pine Street;
Turn right on 16th Street;
}
Else
{
Turn right on 16th Street;
}
Each instruction is on its own line, and the various sets of conditional
instructions are grouped between curly braces and indented for readability.
In C and many other programming languages, the then keyword is implied and
therefore left out, so it has also been omitted in the preceding pseudo-code.
Programming 9
Of course, other languages require the then keyword in their syntax—
BASIC, Fortran, and even Pascal, for example. These types of syntactical
differences in programming languages are only skin deep; the underlying
structure is still the same. Once a programmer understands the concepts
these languages are trying to convey, learning the various syntactical variations
is fairly trivial. Since C will be used in the later sections, the pseudocode
used in this book will follow a C-like syntax, but remember that
pseudo-code can take on many forms.
Another common rule of C-like syntax is when a set of instructions
bounded by curly braces consists of just one instruction, the curly braces are
optional. For the sake of readability, it’s still a good idea to indent these
instructions, but it’s not syntactically necessary. The driving directions from
before can be rewritten following this rule to produce an equivalent piece of
pseudo-code:
Drive down Main Street;
If (street is blocked)
{
Turn right on 15th Street;
Turn left on Pine Street;
Turn right on 16th Street;
}
Else
Turn right on 16th Street;
This rule about sets of instructions holds true for all of the control
structures mentioned in this book, and the rule itself can be described in
pseudo-code.
If (there is only one instruction in a set of instructions)
The use of curly braces to group the instructions is optional;
Else
{
The use of curly braces is necessary;
Since there must be a logical way to group these instructions;
}
Even the description of a syntax itself can be thought of as a simple
program. There are variations of if-then-else, such as select/case statements,
but the logic is still basically the same: If this happens do these things, otherwise
do these other things (which could consist of even more if-then statements).
In the case of our driving directions, Main Street could be under construction.
If it is, a special set of instructions needs to address that situation. Otherwise,
the original set of instructions should be followed. These types of special cases
can be accounted for in a program with one of the most natural control
structures: the if-then-else structure. In general, it looks something like this:
If (condition) then
{
Set of instructions to execute if the condition is met;
}
Else
{
Set of instruction to execute if the condition is not met;
}
For this book, a C-like pseudo-code will be used, so every instruction will
end with a semicolon, and the sets of instructions will be grouped with curly
braces and indentation. The if-then-else pseudo-code structure of the preceding
driving directions might look something like this:
Drive down Main Street;
If (street is blocked)
{
Turn right on 15th Street;
Turn left on Pine Street;
Turn right on 16th Street;
}
Else
{
Turn right on 16th Street;
}
Each instruction is on its own line, and the various sets of conditional
instructions are grouped between curly braces and indented for readability.
In C and many other programming languages, the then keyword is implied and
therefore left out, so it has also been omitted in the preceding pseudo-code.
Programming 9
Of course, other languages require the then keyword in their syntax—
BASIC, Fortran, and even Pascal, for example. These types of syntactical
differences in programming languages are only skin deep; the underlying
structure is still the same. Once a programmer understands the concepts
these languages are trying to convey, learning the various syntactical variations
is fairly trivial. Since C will be used in the later sections, the pseudocode
used in this book will follow a C-like syntax, but remember that
pseudo-code can take on many forms.
Another common rule of C-like syntax is when a set of instructions
bounded by curly braces consists of just one instruction, the curly braces are
optional. For the sake of readability, it’s still a good idea to indent these
instructions, but it’s not syntactically necessary. The driving directions from
before can be rewritten following this rule to produce an equivalent piece of
pseudo-code:
Drive down Main Street;
If (street is blocked)
{
Turn right on 15th Street;
Turn left on Pine Street;
Turn right on 16th Street;
}
Else
Turn right on 16th Street;
This rule about sets of instructions holds true for all of the control
structures mentioned in this book, and the rule itself can be described in
pseudo-code.
If (there is only one instruction in a set of instructions)
The use of curly braces to group the instructions is optional;
Else
{
The use of curly braces is necessary;
Since there must be a logical way to group these instructions;
}
Even the description of a syntax itself can be thought of as a simple
program. There are variations of if-then-else, such as select/case statements,
but the logic is still basically the same: If this happens do these things, otherwise
do these other things (which could consist of even more if-then statements).
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