DCP2073 Asas Pengaturcaraan C Lecture 6: Components of a C Program (Part 3) Lecture 6: C Primitives 6

Topics Type Variables Keywords and Identifiers Assignments Constant Variables Lecture 6: C Primitives 6

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

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)

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 D of D&D

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

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’;

Variable Declaration: Examples int myID; myID

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

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

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

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;

Variable Declaration: Examples 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; “Keywords”

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)

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”

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!)

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

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. */

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

various.c #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'; integer = 33.33; character = 33.33; floatingPoint = 33.33; integer = floatingPoint; floatingPoint = integer; return 0; } various.c

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;

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;

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

“Global” constant variable 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...

Topics Type Variables Keword and Identifiers Assignments Constant Variables

Reading King D&D: Kernighan & Ritchie Chapter 2, 2.4 – 2.8 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