1. 1 Topics Type Variables Keywords and Identifiers Assignments Constant Variables

2. 2 Type The kind of a value is its “type” Not all values are of the same kind –For example: 7 + “cat” makes no sense Value Variable

3. 3 Type Built-in types: char, int, float, double Type modifiers: long, short, const User-defined types (arrays and records) What about “strings”? –Strings are arrays of char (discussed later)

4. 4 Character Representation Characters are stored as a small integer Each character has a unique integer equivalent specified by its position in the ASCII table (pronounced “as-key”) –American Standard Code for Information Interchange

5. 5

6. 6 Character Representation The ASCII values range from 0 to 127 –value 0: special character ’\0’ (a.k.a. NUL character) –value 127: special character –other special characters: ’\n’ ’\t’ ’\’’ ’\\’ etc. –various “extended” sets from 128 to 255

7. 7 Variable Is a logical name for a container –(an actual piece of computer memory for values) Has a type associated with it –tells the computer how to interpret the bits Must be declared before use: int i;float result; int i=0;char initial= ’ K ’ ;

8. 8 Variable Declaration: Examples int myID; myID

9. 9 Variable Declaration: Examples int myID; char myInitial = ’J’; Single “forward quotes” or apostrophe ( ’ ) rather than “back quotes” ( ‘ )

10. 10 Variable Declaration: Examples int myID; char myInitial = ’J’; 01001010 myInitial

11. 11 Variable Declaration: Examples int myID; char myInitial = ’J’; char myInitial = 74 ; 01001010 myInitial

12. 12 Variable Declaration: Examples float commission = 0.05; short int myHeight = 183; /* cm */ long int mySalary = 100000000000000000000; long float chanceOfADate = 3e-500; double chanceOfA2ndDate = 1.5e-500;

13. 13 float commission = 0.05; short int myHeight = 183; /* cm */ long int mySalary = 100000000000000000000; long float chanceOfADate = 3e-500; double chance_of_a_2nd_date = 1.5e-500; Variable Declaration: Examples “Keywords”

14. 14 Keyword...has a special meaning in C...is “case-sensitive”...cannot be used as variable names Examples: int, char, long, main, float, double, const, while, for, if, else, return, break, case, switch, default, typedef, struct, etc.

15. 15 Variable Declaration: Examples float commission = 0.05; short int myHeight = 183; /* cm */ long int mySalary = 100000000000000000000; long float chanceOfADate = 3e-500; double chanceOfA2ndDate = 1.5e-500; “Identifiers”

16. 16 Identifier...is a series of characters consisting of letters, digits and underscores ( _ )...cannot begin with a digit...must not be a keyword...is “case-sensitive” Examples: sUmoFA, x1, y2, _my_ID_, Main (careful!)

17. 17 Assignment Puts a specified value into a specified variable Assignment operator: = = ; not to be confused with ==

18. 18 Assignment: Examples float x = 2.5 ; char ch ; int number ; ch = ’\n’ ; number = 4 + 5 ; /* current value of number is 9. */ number = number * 2; /* current value of number is now 18. */

19. 19 Assignment Value must have a type assignable to the variable Value may be automatically converted to fit the new container Example: –various.c

20. 20 #include /* Do various assignment statements */ int main() { int integer; char character; float floatingPoint; integer = 33; character = 33; floatingPoint = 33; integer = 'A'; character = 'A'; floatingPoint = 'A'; integer = 33.33; character = 33.33; floatingPoint = 33.33; integer = floatingPoint; floatingPoint = integer; return 0; } various.c

21. 21 Constant Variables...are variables that don’t vary...may not be assigned to....must be initialized const float Pi = 3.14159; const int classSize = 100;

22. 22 Constant Variables: Examples const int myID = 192; myID = 666; /* Error! */ const int passMark = 80; short char pAsSgRaDe = ’P’; const float pi = 3.1415926; /* oops */ const double golden_ratio = 1.61803398874989;

23. 23 Converts an angle from degrees to radians output “Enter angle in degrees” input angleInDegrees angleInRadians =  / 180 * angleInDegrees output angleInRadians #include /* Converts an angle in degrees to radians. */ const float PI = 3.1415926; int main() { float angleInDegs; float angleInRads; printf("Enter angle in degrees:"); scanf("%f", &angleInDegs); angleInRads = PI/180*angleInDegs; printf("%f\n", angleInRads); return 0; } Example: Constants

24. 24 Example: Constants “Global” constant variable “Local” variables more on this later... #include /* Converts an angle in degrees to radians. */ const float PI = 3.1415926; int main() { float angleInDegs; float angleInRads; printf("Enter angle in degrees: "); scanf("%f", &angleInDegs); angleInRads = PI/180*angleInDegs; printf("%f\n", angleInRads); return 0; }