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

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Value may be automatically converted to fit the new ... Converts an angle from degrees to radians. output 'Enter angle in degrees' input angleInDegrees ... – PowerPoint PPT presentation

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


1
CSE1301Computer ProgrammingLecture
6Components 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 cant logically evaluate 7 cat

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 DD

6
(No Transcript)
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 ltDELgt
  • 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 lttype namegt ltvariable namegt
modifiers lttype namegt ltvariable namegt ltinit
valuegt
9
Variable Declaration Examples
  • int 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

12
Variable Declaration Examples
  • int myID
  • char my_initial J
  • char my_initial 74

13
Variable Declaration Examples
  • float commission 0.05
  • short int myHeight 165 / cm /
  • long int mySalary 100000000000000000000
  • long float chanceOfADate 3e-500
  • double chance_of_a_2nd_date 1.5e-500

14
Variable Declaration Examples
  • float commission 0.05
  • short int myHeight 165 / cm /
  • long int mySalary 100000000000000000000
  • long float chanceOfADate 3e-500
  • double chance_of_a_2nd_date 1.5e-500

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 DD
    2/e Appendix A or DD 3/e page 545, Figure 15.4)

16
Variable Declaration Examples
  • float commission 0.05
  • short int myHeight 165 / cm /
  • long int mySalary 100000000000000000000
  • 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

ltvariable namegt ltexpressiongt
19
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. /
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 ltstdio.hgt
  • / 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 dont vary
  • ...may not be assigned to.
  • ...must be initialized

const modifiers lttypegt ltconstant namegt ltinit
valuegt
23
Constant Variables Examples
  • const int myID 192
  • myID 666 / Error! /

const int passMark 80 short char pAsSgRaDe
P const float e 3.1415926 / oops
/ const double golden_ratio 1.61803398874989
24
Example Constants
include ltstdio.hgt / Converts an angle in
degrees to radians. / const float PI
3.1415926 int main() float
angleInDegrees float angleInRadians
printf("Enter angle in degrees ")
scanf("f", angleInDegrees) angleInRadians
PI / 180 angleInDegrees
printf("f\n", angleInRadians) return 0
  • Converts an angle from degrees to radians
  • output Enter angle in degrees
  • input angleInDegrees
  • angleInRadians ? / 180 angleInDegrees
  • output angleInRadians

25
Example Constants
include ltstdio.hgt / Converts an angle in
degrees to radians. / const float PI
3.1415926 int main() float
angleInDegrees float angleInRadians
printf("Enter angle in degrees ")
scanf("f", angleInDegrees) angleInRadians
PI / 180 angleInDegrees
printf("f\n", angleInRadians) return 0
Global (constant) variable
Local variables
more on this later...
26
Readings
  • This Lecture
  • DD 2/e Sections 2.1 to 2.10
  • DD 3/e Sections 2.1 to 2.5
  • Next Lecture Booleans
  • DD 2/e
  • Sections 2.12 to 2.13, 3.2 and 4.13 to 4.15
  • DD 3/e Sections 2.6, 3.5, 4.10 and 4.11
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