Variables in C

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 3.14159 ) • 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 • int long • register return • short signed • sizeof static • struct switch • typedef union • unsigned void • volatile while • auto break • case char • const continue • default do • double else • enum extern • float for • goto if

11. Which Are Legal Identifiers ? • AREA area_under_the_curve • 3D num45 • Last-Chance #values • x_yt3 pi • num$ %done • lucky***

12. Declarations and assignmentswreck.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); • }