- Built-in data types:
these types come with the language and you can use them
without having to "define" them
- User-defined data types (classes): these data types are defined by the programmer to serve some purpose in his program
| Syntax | Name | use |
|---|---|---|
| char | character | Character or very short integer (-128..127) |
| short | short integer | uses 2 byte memory, value between -32768 and 32767 |
| int | ordinary integer | uses 4 byte memory, value between -2147483648 and 2147483647 |
| long | long integer | uses 8 bytes memory, value between -9223372036854775808 and 9223372036854775807 |
| float | single precision float | uses 4 byte memory, absolute value between 1.4E-45 and 3.4E38 |
| double | double precision float | uses 8 byte memory, absolute value between 4.9E-324 and 1.8E308 |
| bool | boolean | true (1) or false (0) |
- Variables and/or constants of the
same bulit-in type
can be
combined "naturally"
- i.e.,
without having to perform any conversion operations
-
in operations such as +, -, * or /
- Example:
float A, B, C; - Defines 3 float variables A = 4; B = 5; C = A + B;
This is the similar situation as "adding apples and apples".
- Variables and/or constants of the
different bulit-in type
CANNOT be combined
WITHOUT having to perform any conversion operations FIRST !!!
-
in operations such as +, -, * or /
- Example:
int A; - Defines integer float B, C; - Defines 2 float variables A = 4; // Integer B = 5; // Float C = A + B; - value of A is converted to FLOAT first !!!
This is the similar situation as "adding apples and oranges". We must convert the apples to oranges first before we can add
-
Example Program:
(shows type conversion) ---
click here
- Save the program
- Compile using: CC -S type-conv.C
- Look at the output using: vi type-conv.s
- Notice the additional instructions needed to convert the integer A2 to a float value before the addition (floating add - fadds) can take place.
- As you have seen, the computer can convert
one data type to another data type.
- But not all conversions are
safe
- The following conversions are safe because the destination type
contains all values of the original type:
- Difference C++ and Java:
- C/C++ will automatically
perform
all (safe and unsafe) conversions
as needed
- In Java, the programmer must use casting operation to request unsafe conversions
Warning:
-
In C++, you can perform
unsafe assignments
that Java will not allow
without casting
(C++ is designed for system programming; and system programmers prefer to have access to all features of the computer.
Compiler checks often limit the programmers' ability to perform some tasks.
Hence, C++ compilers are less strongly typed than Java)
Example:
int i; short s; i = 9827563; s = i; // <-- This conversion is allowed in C++ // without casting !!!
- C/C++ will automatically
perform
all (safe and unsafe) conversions
as needed
-
Example Programs:
(convert a higher type to a lower type) --
click here
-
A similar program in Java:
(convert a higher type to a lower type) --
click here
- Just like Java,
you can define your own
date type
in C++ using the
class
construct.
- Structure of the class
definition is similar to Java:
class CLASSNAME { variable definitions function (method) definitions }Example:
class my_int { int value; // Member variable };
The similarity is quite deceiving; because the underlying representation of objects is completely different
However, we need to delay this and study the fundaments of C++ first.
We will look at this much later...