Announcements

1
Announcements

• Programming assignment 1 is due by midnight.
• Late submissions accepted until Sunday midnight
• Quiz 1 is due by midnight.
• NO late submissions accepted
• Grade posting ID will be emailed to your engr
  address (next week).
• Programming Assignment 2 is available on the
  course web page.
• Due Friday, 10/17, by midnight.

2
A Correction

• Last time I said that to print a symbol you
  can use \
• This is wrong, need to say
• int n 37
• printf("here is 10 of d f", n, n0.10)

3
Lexical Analysis - Tokens

• Keywords
• e.g int, return
• Identifiers
• e.g main, square, cube, PI
• Numeric literal constants
• e.g. 3 3.14159 -12
• String literal constants
• e.g. "Hello world\n"
• Operators
• e.g. - / ( )
• Punctuators
• e.g. , ( )

4
Identifiers

• Letters, digits, and underscore, '_'
• Must start with letter or underscore.
• Upper or lower case, but identifiers are case
  sensitive.
• Used for names of variables, symbolic constants,
  and functions.
• Should be abstract
• Named for what they represent
• Meaningful

5
Identifiers

• Correct
• myName, ticket_Count, acctBalance, _code
• Syntactically correct, but not good
• x, xyz, c2, __p
• Incorrect
• Not-good, 1size, my name, __

6
Literal and symbolic numeric constants

• Integer literal constants
• e.g. 0 1 -5 320000
• decimal (base 10) 128
• octal (base 8) 0200
• hexadecimal (base 16) 0x80
• Floating point (real) literal constants
• e.g. 1.5 3.14
• Symbolic constants
• e.g. define PI 3.14159
• e.g. define MAX 600

7
String literal constants

• Any character you can type inside
• e.g. This is a literal constant
• The backslash character \
• Used to include white space in strings
• \n represents New Line character
• \t represents Tab character
• Used to include " and \
• \" represents "
• \\ represents \
• e.g. \tA \literal\ with a \\ and a \nnew
  line.
• Which would display as
• A literal with a \ and a
• new line.

8
Literal and symbolic string constants

• Literal
• printf("You've made an error\n")
• Symbolic
• define ERRMSG "You've made an error\n"
• printf(ERRMSG)

9
Literal and symbolic character constants

• Character literal constants
• e.g. A a 5
• Symbolic constants
• e.g. define AT _at_
• e.g. define NEWLINE \n

10
The ASCII Code

• American Standard Code for Information
  Interchange.
• Each character is assigned a code (number).
• ASCII codes go from 0 to 255
• 0 - 31 are control codes
• 32 - 126 are keyboard characters
• 65 90 are capital letters
• 97 122 are lower-case letters
• 48 57 are digits 0 9
• 127 is delete character
• 128 255 are graphics characters

11
Characters are not Strings

• "A" is stored and treated differently from 'A'
• A is stored as two bytes 65 and 0
• A is stored as 65 only.
• "abc" is a legal string
• 'abc' is illegal -- a char variable or constant
  is always only ONE character.

12
Non-printing and hard-to-print character constants

• '\n' is new line character (two symbols represent
  only one character, ASCII 10).
• '\t' is tab character (ASCII 9).
• '\"' is double quote character
• '\\' is backslash character ('\' doesnt work,
  '\\' must be used)

13
Variables

• Memory location to store data.
• Must be declared before used.
• Declaration includes type and name.
• Basic numeric types are int, float (small real),
  double (large real), char (small integer).

14
Variable Declaration Examples

• int n / integers are stored in 4 bytes /
• / roughly -2 billion to 2 billion /
• int a, b 0 / note initialization along with
  declaration /
• float x 3.5, y / stored in 4 bytes /
• / 6 or 7 significant digits /
• double z 3.14159265358979 / stored in 8
  bytes /
• / 15 significant digits /
• char c 'A' / stored in one byte /
• / characters are numbers -- more about this
  later /

15
Operators Punctuators

• Arithmetic (binary) - /
• e.g. a b, 5 2
• Arithmetic (unary) -
• e.g. 25, -30
• Assignment (binary)
• e.g. n 5
• Grouping, etc. ( ) ,

16
Expressions

• Expression -- Any combination of identifiers,
  constants, operators and punctuators.
• e.g. (a b) 3 - 20 / 3

17
Precedence

• Precedence rank or priority.
• Some operators have priority over others (i.e
  should be done first)
• 1 2 3 same as 1 (2 3) (i.e. 7)
• has higher precedence than binary or -
• Parentheses force precedence.
• (1 2) 3 is equal to 9

18
Associativity

• When operators have same precedence we must use
  rules of associativity (left to right or right to
  left)
• - same precedence, left to right assoc.
• 123-45 means (((12)3)-4)5 7
• / same precedence, left to right assoc.
• 4 / 2 3 means (4/2)3 6 not 4/(23) 0
  ...

19
Precedence /Associativity Table

• operation precedence associativity
• ( ) 1 L to R
• unary , unary - 2 R to L
• / 3 L to R
• - 4 L to R
• (assignment) 5 R to L

20
Use Parentheses!!!!!!!!

• Best to force precedence and associativity with
  parentheses.
• Easier to read
• Everyone gets confused about these rules!

21
Increment, Decrement

• Unary increment and decrement (highest
  precedence)
• a --a ('pre' versions)
• a a-- ('post' versions)
• Value in memory is incremented or decremented by
  one.
• Pre Version - value changed then used.
• Post Version - value used then changed. ...

22
Increment, Decrement Examples

• Let b 2 and c 3.
• After assignment a (b) (c)
• the values will be a7, b3, c4
• Let b 2 and c 3.
• After the assignment a (b) (c)
• the values will be a5,b3,c4
• --i is a legal statement.
• Same as i i - 1
• Avoid expressions like
• a c c

23
Assignment Operator

• An assignment has a value!
• a (b 0) same as a0 b0
• or a b 0 (because of right to left
  associativity).
• a (b 2) (c 3) is legal but not very
  readable.
• Don't do it! (c is 3, b is 2 and a is 5)

24
Shortcut Assignment

• a 5 means a a 5
• Similarly
• a - 5 means a a - 5
• a 5 means a a 5
• a / 5 means a a / 5
• a 5 means a a 5

25
Statements

• Simple Statement is an expression followed by a
  semicolon.
• val val - 1 / assignment statement/
• printf("d miles", val) / function call
  statement /
• Compound Statement block, i.e. multiple
  statements surrounded by braces (curly brackets).
• int main(void)
• int a 5
• printf("d", a)
• a a - 1
• return 0

compound statement
26
Inputting Value from KB

• The function scanf() waits for input from
  keyboard.
• Very important
• the variables that will store the input values
  must be designated with
• Input can be integer (d), float (f),
  double(lf), char (c) or string (s).
• scanf(string, var1, var2, )

string contains conversion specifiers for var1,
var2, etc.
27
Input Example
include ltstdio.hgt int main(void) int
a float x double z scanf("d f lf", a,
x, z) printf("d\nf\nf\n", a, x,
z) return 0
28
printf formatting

• f can be used to print either float or double
  variables.
• Real number output formatting, n.mf
• m specifies number of digits to right of decimal
• n specifies minimum width of printing field
• if n is negative, then output is left justified
  in field

29
Formatting Example

• If x 3.1415926 then printf("10.3f",x) will
  print
• 3.142
• But printf("0.3f", x) prints
• 3.142

m3 printing spaces
n10 printing spaces
30
Printing Integers and Strings

• Integers and strings can also use field width
• nd, ns where n is again min field width.
• Example printf("-10d10s", 21,"abcde")
• 21 abcde

8 wide
5 wide
10 wide
10 wide
31
Legal vs. Correct Program

• The compiler forces you to make a legal program
  -- one that obeys the grammar rules.
• It is up to you to make sure the program is
  correct -- that it solves the given problem.

32
Find the 9 Errors
include ltstdiogt define TOPBOTTOM "III"
define MIDDLE "\nI" void main(void)
printf("/n/n/n") printf(TOPBOTTON) printf(MID
DLE) printf(MIDDLE) printf(\n) prinf(TOPBOTTO
M) return 1
33
Some other useful functions

• These all require include ltctype.hgt
• isalpha(c) - returns true if c is letter
• isdigit(c) - returns true if c is a digit (0-9)
• isspace(c) - returns true if c is space, tab or
  newline.
• islower(c) - returns true if c is lower case.
• isupper(c) - returns true if c is upper case.

34
Change to Caps

• Change input letters to caps
• Difference between lower case and upper case is
  32 for all letters (in English).
• 'a' - 'A' has value 32
• 'z' - 'Z' also has value 32

35
ToUpper

• int main(void)
• char c1,c2,c3,c4,c5
• c1 getchar() c2 getchar() / get the chars
  /
• c3 getchar() c4 getchar() c5
  getchar()
• / convert to UC and print /
• printf("\n\nccccc",
• toupper(c1), toupper(c2), toupper(c3),
• toupper(c4), toupper(c5))
• / print as characters /
• return 0

36
Questions?

• Read Chapter 4.1 4.6