From 7e0f021a9aec35fd8e6725e87e3313b101d26f5e Mon Sep 17 00:00:00 2001 From: Tobias Klauser Date: Sun, 27 Jan 2008 11:37:44 +0100 Subject: Initial import (2.0.2-6) --- reference/C/CONCEPT/data_types.html | 218 ++++++++++++++++++++++++++++++++++++ 1 file changed, 218 insertions(+) create mode 100644 reference/C/CONCEPT/data_types.html (limited to 'reference/C/CONCEPT/data_types.html') diff --git a/reference/C/CONCEPT/data_types.html b/reference/C/CONCEPT/data_types.html new file mode 100644 index 0000000..1c32515 --- /dev/null +++ b/reference/C/CONCEPT/data_types.html @@ -0,0 +1,218 @@ +C Data types + +

+ +

C Data types.

+ +

Variable definition

+C has a concept of 'data types' which are used to +define a variable +before its use.

+The definition of a variable will assign storage for the variable and +define the type of data that will be held in the location.

+So what data types are available? +

+ + +
int + float + double + char + void + enum +
+

+Please note that there is not a boolean data type. C does not have the +traditional view about logical comparison, but thats another story.

+ +Recent C++ compilers do have a boolean datatype. +

+ +

int - data type

+int is used to define integer numbers. +

+ +

+
+    {
+        int Count;
+        Count = 5;
+    }
+

+ +

float - data type

+float is used to define floating point numbers. +

+ +

+
+    {
+        float Miles;
+        Miles = 5.6;
+    }
+

+ +

double - data type

+double is used to define BIG floating point numbers. It reserves twice +the storage for the number. On PCs this is likely to be 8 bytes. +

+ +

+
+    {
+        double Atoms;
+        Atoms = 2500000;
+    }
+

+ +

char - data type

+char defines characters. +

+ +

+
+    {
+        char Letter;
+        Letter = 'x';
+    }
+

+ +

Modifiers

+The three data types above have the following modifiers. +

short +
long +
signed +
unsigned +

+ +The modifiers define the amount of storage allocated to the variable. +The amount of storage allocated is not cast in stone. ANSI has the +following rules:

+ +

+
+        short int <=    int <= long int
+            float <= double <= long double
+

+ +

+What this means is that a 'short int' should assign less than or the same +amount of storage as an 'int' and the 'int' should be less or the same bytes +than a 'long int'. What this means in the real world is: +

+ + +
+
+ + Type Bytes Bits Range +
+
+
+ + short int 2 16 -16,384 -> +16,383 (16kb) + unsigned short int 2 16 0 -> +32,767 (32Kb) + unsigned int 4 16 0 -> +4,294,967,295 ( 4Gb) + int 4 32 -2,147,483,648 -> +2,147,483,647 ( 2Gb) + long int 4 32 -2,147,483,648 -> +2,147,483,647 ( 2Gb) + signed char 1 8 -128 -> +127 + unsigned char 1 8 0 -> +255 + float 4 32 + double 8 64 + long double 12 96 +
+
+

+These figures only apply to todays generation of PCs. Mainframes and +midrange machines could use different figures, but would still comply +with the rule above.

+You can find out how much storage is allocated to a data type by using +the sizeof operator. + +

Qualifiers

const +
volatile +

+ +The const qualifier is used to tell C that the variable value can not +change after initialisation.

+ + const float pi=3.14159; + +

+pi cannot be changed at a later time within the program.

+Another way to define constants is with the +#define preprocessor which +has the advantage that it does not use any storage (but who counts bytes + these days?).