Transcript LECT12.PPT

Variables in C
Declaring ,
Naming, and
Using Variables
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Using Variables
You may declare variables in C.
 The declaration includes the data type
you need.
 Examples of variable declarations:

int meatballs ;
float area ;
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Declaring Variables

When we declare a variable:
o space in memory is set aside to hold that
data type
o That space is associated with the variable
name
o Visualization of the declaration
int meatballs ;
meatballs
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Legal Variable Names

Variable names in C must be valid
identifiers
o Consists of letters, digits and underscores.
o May be as long as you like, but only the
first 31 characters are significant.
o May NOT begin with a number
o May not be a C keyword
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Naming Conventions
Begin variable names with lowercase
letters
 Use meaningful identifiers
 Separate “words” within identifiers with
underscores or mixed upper and lower
case.
 Example: surfaceArea surface_Area
or surface_area
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 Be consistent !!

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Naming Conventions
(continued)

Use all uppercase for symbolic
constants ( #define )
Example: PI (#define PI 3.14159 )

Function names follow the same rules
as variables
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Case Sensitive

C is case sensitive
o It matters whether something is upper or
lower case
o Example: area is different than Area
which is different than AREA
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More About Variables
C has 3 basic predefined data types
 Integers

o int, long int, short int, unsigned int

Floating point numbers
o float, double

Characters
o char
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Initializing Variables

Variables may be initialized
o int x = 7;
o float y = 5.9;
o char c = ‘A’;

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Do not “hide” the initialization
o put initialized variables on a separate line
o a comment is probably a good idea
o int y = 6; /* feet per fathom */
o NOT int x, y = 6, z;
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Keywords in C

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auto
case
const
default
double
enum
float
goto
break
char
continue
do
else
extern
for
if
int
register
short
signed
sizeof
struct
typedef
unsigned
volatile
long
return
static
switch
union
void
while
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Which Are Legal Identifiers ?
AREA
3D
Last-Chance
x_yt3
num$
lucky***
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area_under_the_curve
num45
#values
pi
%done
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Declarations and assignments
wreck.c
#include <stdio.h>
main ( )
{
int inches, feet, fathoms ;
fathoms = 7 ;
feet = 6 * fathoms ;
inches = 12 * feet ;
inches
feet
fathoms
fathoms
7
feet
42
inches
504
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}
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wreck.c (cont’d)
main ( )
{



printf (“Its depth at sea: \n”) ;
printf (“ %d fathoms \n”, fathoms) ;
printf (“ %d feet \n”, feet);
printf (“ %d inches \n”, inches);
}
%d is a place holder - indicates that the
value of the integer variable is to be printed in
decimal form (rather than binary or hex) at
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Floating point numbers
Are numbers that can contain decimal
points.
 What if the depth were really 5.75
fathoms ? ... Our program, as it is,
couldn’t handle it.
 We can declare floating point variables
like this :
float fathoms ;
float feet ;

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Floating point version of wreck.c
(works for any depth shipwreck)
#include <stdio.h>
main ( )
{
float fathoms, feet;
printf (“Enter the depth in fathoms : ”);
scanf (“%f”, &fathoms);
feet = 6.0 * fathoms;
printf (“She’s %f feet down.\n”, feet);
}
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