Slides adopted from T. Ferguson Spring 2016

Transcription

1 CSE1311 Introduction to Programming for Science & Engineering Students Mostafa Parchami, Ph.D. Dept. of Comp. Science and Eng., Univ. of Texas at Arlington, USA Slides adopted from T. Ferguson Spring 2016

2 Topics Type Variables Keywords and Identifiers Assignments Constant Variables 2

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 3

4 Types 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) 4

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 American Standard Code for Information Interchange see Appendix D of D&D 5

6 Topics 6

7 Variables 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; int i=0; float result; char initial= K ; 7

8 Variable Declaration int myid; myid 8

9 Variable Declaration int myid; char myinitial = J ; Single forward quotes or apostrophe ( ) rather than back quotes ( ) 9

10 Variable Declaration int myid; char myinitial = J ; myinitial 10

11 Variable Declaration int myid; char myinitial = J ; char myinitial = 74 ; myinitial 11

12 Variable Declaration Examples float commission = 0.05; short int myheight = 183; /* cm */ long int mysalary = ; long float chanceofadate = 3e-500; double chanceofa2nddate = 1.5e-500; 12

13 Variable Declaration Examples Keywords float commission = 0.05; short int myheight = 183; /* cm */ long int mysalary = ; long float chanceofadate = 3e-500; double chance_of_a_2nd_date = 1.5e-500; 13

14 Keyword 1....has a special meaning in C 2....is case-sensitive 3....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 3/e page 545, Figure 15.4) 14

15 Variable Declaration Examples float commission = 0.05; Identifiers short int myheight = 183; /* cm */ long int mysalary = ; long float chanceofadate = 3e-500; double chance_of_a_2nd_date = 1.5e-500; 15

16 Variable Declaration Examples 16

17 Identifier...is a series of characters consisting of letters, digits and underscores (_) 1....cannot begin with a digit 2....must not be a keyword 3....is case-sensitive Examples: sumofa, x1, y2, _my_id_, Main (careful!) 17

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

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. */ 19

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

21 #include <stdio.h> /* Do various assignment statements */ int main() { int integer; char character; float floatingpoint; integer = 33; character = 33; floatingpoint = 33; } integer = 33.33; character = 33.33; floatingpoint = 33.33; integer = floatingpoint; floatingpoint = integer; return 0; integer = 'A'; character = 'A'; floatingpoint = 'A'; various.c 21

22 Constant Variables...are variables that don t vary...may not be assigned to....must be initialized const float Pi = ; const int classsize = 100; 22

23 Constant Variable Examples const int myid = 192; myid = 666; /* Error! */ const int passmark = 80; const char passgrade = P ; const float pi = ; const double golden_ratio = ; 23

24 Example Convert an angle from degrees to radians Algorithm: 1) output Enter angle in degrees 2) input angleindegrees 3) angleinradians = π / 180 * angleindegrees 4) output angleinradians 24

25 Converts an angle from degrees to radians output Enter angle in degrees input angleindegrees Example #include <stdio.h> /* Converts an angle in degrees to radians. */ const float PI = ; int main() { float angleindegs; float angleinrads; angleinradians = π / 180 * angleindegrees output angleinradians } printf("enter angle in degrees:"); scanf("%f", &angleindegs); angleinrads = PI/180*angleInDegs; printf("%f\n", angleinrads); return 0; 25