1. Variables in C
Declaring ,
Naming, and
Using Variables

2. Using Variables You may declare variables in C.
The declaration includes the data type you need.
Examples of variable declarations:
int meatballs ;
float area ;

3. Declaring Variables When we declare a variable:
space in memory is set aside to hold that data type
That space is associated with the variable name
Visualization of the declaration
int meatballs ;
meatballs
FE07

4. Legal Variable Names Variable names in C must be valid identifiers
Consists of letters, digits and underscores.
May be as long as you like, but only the first 31 characters are significant.
May NOT begin with a number
May not be a C keyword

5. 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
Be consistent !!

6. Naming Conventions (continued)
Use all uppercase for symbolic constants ( #define )
Example: PI (#define PI )
Function names follow the same rules as variables

7. Case Sensitive C is case sensitive
It matters whether something is upper or lower case
Example: area is different than Area which is different than AREA

8. More About Variables C has 3 basic predefined data types Integers
int, long int, short int, unsigned int
Floating point numbers
float, double
Characters
char

9. Initializing Variables
Variables may be initialized
int x = 7;
float y = 5.9;
char c = ‘A’;
Do not “hide” the initialization
put initialized variables on a separate line
a comment is probably a good idea
int y = 6; /* feet per fathom */
NOT int x, y = 6, z;

10. Keywords in C auto break case char const continue default do
double else
enum extern
float for
goto if
int long
register return
short signed
sizeof static
struct switch
typedef union
unsigned void
volatile while

11. Which Are Legal Identifiers ?
AREA area_under_the_curve
3D num45
Last-Chance #values
x_yt pi
num$ %done
lucky***

12. Declarations and assignments wreck.c
inches
#include <stdio.h>
main ( ) {
int inches, feet, fathoms ;
fathoms = 7 ;
feet = 6 * fathoms ;
inches = 12 * feet ; }
feet
fathoms
fathoms 7
feet 42
inches
504

13. 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 that location.

14. 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 ;

15. 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); }