1. CMSC 104, Section 4 Richard Chang
Variables in C
CMSC 104, Section 4
Richard Chang
[Based on dblock spr’06lecture, heavily modified, reordered, many new slides added]

2. What Are Variables in C?
Variables in C are similar to variables in algebra.
x = a + b
z + 2 = 3(y - 5)
However, variables in C represent storage locations.

3. Rules for Variable Names
C variables can have multiple characters
Legal variable names in C
May only consist 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 reserved word (keyword)

4. Reserved Words (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

5. Naming Conventions Begin variable names with lowercase letters
Use meaningful identifiers (names)
Separate “words” within identifiers with underscores or mixed upper and lower case.
Examples: surfaceArea surface_Area surface_area
Be consistent!

6. Case Sensitivity
It matters whether an identifier, such as a variable name, is uppercase or lowercase.
Example:
area Area AREA ArEa
are all seen as different variables by the compiler.
Pick one.

7. Legal Identifiers vs. Naming Conventions
Legal identifiers refer to the restrictions C places on naming identifiers.
Naming conventions refer to the standards you must follow for this course.
Just because you can, does not make it a good idea!

8. Which Are Legal Identifiers?
AREA D
lucky*** num45
Last-Chance #values
x_yt3 pi
num$ %done
area_under_the_curve

9. finaltotal numChildren area_under_the_curve
Which are good ideas?
Area person1
Last_Chance values
x_yt pi
finaltotal numChildren
area_under_the_curve

10. Declaring Variables
Before using a variable, you must give the compiler some information about the variable; i.e., you must declare it.
The declaration statement includes the data type of the variable.
Examples of variable declarations:
int meatballs ;
double area ;

11. More About Variables C has three basic predefined data types:
Integers (whole numbers)
int, long int, short int, unsigned int
Floating point (real numbers)
float, double
Characters
char

12. Using Variables: Initialization
Variables may be be given initial values, or initialized, when declared. Examples:
int length = 7 ;
double diameter = 5.9 ;
char initial = ‘A’ ;
diameter
initial 7
5.9
‘A’
length

13. Using Variables: Assignment
Values are assigned to variables using the assignment operator =
This operator does not denote equality
Examples:
diameter = 5.9 ; area = length * width ;
Only single variables may appear on the left side of the assignment operator.

14. Example: Declarations and Assignments
#include <stdio.h>
int main( ) {
int inches, feet, fathoms ;
fathoms = 7 ;
feet = 6 * fathoms ;
inches = 12 * feet ;
inches
garbage
feet
garbage
fathoms
garbage
fathoms 7
feet 42
inches
504

15. Example: Declarations and Assignments (cont’d)
printf (“Its depth at sea: \n”) ;
printf (“ %d fathoms \n”, fathoms) ;
printf (“ %d feet \n”, feet) ;
printf (“ %d inches \n”, inches) ;
return 0 ; }