1 CSE1301 Computer Programming Lecture 6: Components of a C Program (Part 2)

2 Topics Type Variables Keywords and Identifiers Assignments Constant Variables

3 Type The kind of a value is its “type” Not all values are of the same kind –For example: can’t logically evaluate 7 + “cat” 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 “ask-key”) –American Standard Code for Information Interchange –see Appendix D of D&D

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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) Have a type associated with them, which tells the computer how to interpret the bits Must be declared before use: [modifiers] ; [modifiers] = ;

9 Variable Declaration: Examples int myID; myID

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

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

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

13 Variable Declaration: Examples float commission = 0.05; short int myHeight = 165; /* cm */ long int mySalary = ; long float chanceOfADate = 3e-500; double chance_of_a_2nd_date = 1.5e-500;

14 float commission = 0.05; short int myHeight = 165; /* cm */ long int mySalary = ; long float chanceOfADate = 3e-500; double chance_of_a_2nd_date = 1.5e-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 D&D 3/e page 545, Figure 15.4)

16 Variable Declaration: Examples float commission = 0.05; short int myHeight = 165; /* cm */ long int mySalary = ; long float chanceOfADate = 3e-500; double chance_of_a_2nd_date = 1.5e-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 Constant Variables...are variables that don’t vary...may not be assigned to....must be initialized const [modifiers] = ;

23 Constant Variables: Examples const int myID = 192; myID = 666; /* Error! */ const int passMark = 80; short char pAsSgRaDe = ’P’; const float e = ; /* oops */ 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 angleInDegrees; float angleInRadians; printf("Enter angle in degrees: "); scanf("%f", &angleInDegrees); angleInRadians = PI / 180 * angleInDegrees; printf("%f\n", angleInRadians); 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 angleInDegrees; float angleInRadians; printf("Enter angle in degrees: "); scanf("%f", &angleInDegrees); angleInRadians = PI / 180 * angleInDegrees; printf("%f\n", angleInRadians); return 0; }

26 Readings This Lecture: D&D 2/e: Sections 2.1 to 2.10 D&D 3/e: Sections 2.1 to 2.5 Next Lecture: Booleans D&D 2/e: –Sections 2.12 to 2.13, 3.2 and 4.13 to 4.15 D&D 3/e: Sections 2.6, 3.5, 4.10 and 4.11