Data Types - dooncomputing

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Int 2 Computing
Software Development
High Level Language Constructs
I Power
Simple Data Types
Some of the types of variables used include:
String
Real
Integer
Boolean
Strings
String variables contain text and can take up
a range of memory.
Two operations that can be applied are:
Concatenation.
Substrings.
Concatenation
Concatenation is the addition of two strings.
One string is placed at the end of the other.
Forename$ = “Bob”
Surname$= “Jones”
Fullname$ = Forename$ + Surname$
The Variable Fullname$ will now contain:
“BobJones”
Substrings
Substrings are often referred to as string
slicing.
This is where the part of the string is
extracted.
A Variable Fullname$ may contain:
“BobJones”
Forename$ := Fullname$(1:3)
Surname$ := Fullname$(4:8)
Forename$ now contains “Bob” and
Surname$ now contains “Jones”
Real
Real numbers are floating point numbers.
They usually use 32bits of computer
memory.
Remember:
E.g. 20.125 = .20125 x 100 = .20125 x102
Any number can be represented in the form:
M x basee
Where M is the mantissa and e is the
exponent.
Integer
An Integer is any positive or negative whole
number.
Integers usually use 32bits of computer
memory.
All mathematical operations can be applied
to these numbers.
E.g. + - x /
Boolean
A Boolean value can have either the value
True or False.
Their value is stored using one bit of
memory.
Logical operators can be used on Booleans
E.g. AND, OR, NOT.
Arrays
This is a set of data items of the same type
grouped together with a single variable
name.
Each Data item (Element) in the array is
identified by the variable name and a
subscript (index).
An array of names may look like this:
Name(1) Contains John
Name(2) Contains Helen
Name(2) Contains Peter
Decision Making
All languages have some decision-making
construct.
IF, where the execution of an action
depends on a stated condition.
Most languages expand this to allow for a
series of outcomes using:
IF…THEN…ELSE…
Decision Making (Cont.)
Nested IF
IF mark >= 70 then
PRINT “A”
ELSE IF mark >= 60 then
PRINT “B”
ELSE IF mark >= 50 then
PRINT “C”
ELSE IF mark >= 45 then
PRINT “D”
ELSE
PRINT “No Award”
END IF
Modules
Modules can take many different form
depending on the language.
Functions; This is similar to a subroutine
except that it has a value that can be assigned
rather than returning a variable.
Parameter passing by value
(In Parameter)
When a parameter is passed by value into a
subroutine an exact copy of current value of
the original variable is used by the
subroutine.
This allows one-way data transfer between
the main program and the subroutine.
The programmer can then guarantee that the
variable will still be suitable for other parts
of the code.
Passing by value (Example)
The Value of the parameter stored at 5000
location 5000 is passed by value. 5001
5002
A copy of the value is stored at
location 5001
The subroutine is then free to change
the value in 5001
The value of the original remains
unchanged.
Simon
Simon
Paul
Memory
Locations
Parameter Passing by Reference
(In/Out Parameter)
Parameter passing by reference allows the
data that is passed into a subroutine to be
changed, then passed back out to other parts
of the program.
This allows a two way data transfer between
the main program and the subroutine.
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