1 CSE1301 Computer Programming Lecture 6 C Primitives 3

2 Topics Type Variables Keywords and Identifiers Assignments Constants

3 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

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

5 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 –see Appendix E of King

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7 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

8 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 ’ ;

9 Variable Declaration: Examples int myID; myID

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

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

12 Variable Declaration: Examples int myID; char myInitial = ’J’; char myInitial = 74 ; myInitial

13 Variable Declaration: Examples short int myHeight = 152; /* cm */ int mySalary = ; long int mySalary = ; float commission = 0.05; double chanceOfADate = 3e-500;

14 short int myHeight = 152; /* cm */ int mySalary = ; long int mySalary = ; float commission = 0.05; double chance_of_a_date = 3e-500; Variable Declaration: Examples “Keywords”

15 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. (see D&D 2/e Appendix A or King page 24)

16 Variable Declaration: Examples short int myHeight = 152; /* cm */ int mySalary = ; long int mySalary = ; float commission = 0.05; double chanceOfADate = 3e-500; “Identifiers”

17 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!)

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

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

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

21 #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

22 Constants don’t vary may not be assigned to must be initialized const float Pi = ; const int classSize = 100;

23 Constants: Examples const int myID = 192; myID = 666; /* Error! */ const int passMark = 80; const char pAsSgRaDe = ’P’; const float pi = ; const double golden_ratio = ;

24 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 = ; 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

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

26 Topics Type Variables Keword and Identifiers Assignments Constant Variables

27 Reading King –Chapter 2, 2.4 – 2.8 –Chapter 4, 4.2 – 4.5 –Chpater 7, 7.1 – 7.3 D&D: –Chapter 9, 9.1 – 9.5, 9.11 Kernighan & Ritchie –2.4 – 2.8, 2.10, 2.12