1 / 24

Topics

Topics. Type Variables Keywords and Identifiers Assignments Constant Variables. Variable. Value. Type. The kind of a value is its “type” Not all values are of the same kind For example: 7 + “cat” makes no sense. Type. Built-in types: char , int , float, double

tacy
Download Presentation

Topics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

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

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

  6. 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’;

  7. myID Variable Declaration: Examples int myID;

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

  9. 01001010 myInitial Variable Declaration: Examples int myID; char myInitial = ’J’;

  10. 01001010 myInitial Variable Declaration: Examples int myID; char myInitial = ’J’; char myInitial = 74 ;

  11. 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;

  12. Variable Declaration: Examples “Keywords” 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;

  13. 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.

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

  15. 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!)

  16. not to be confused with == Assignment • Puts a specified value into a specified variable • Assignment operator: = <variable name> = <expression> ;

  17. 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. */

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

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

  20. 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;

  21. 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;

  22. Example: Constants #include <stdio.h> /* 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; } Converts an angle from degrees to radians output “Enter angle in degrees” input angleInDegrees angleInRadians =  / 180 * angleInDegrees output angleInRadians

  23. Example: Constants #include <stdio.h> /* 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; } “Global” constant variable “Local” variables more on this later...

More Related