Wavelet transform And Its Applications to Image Processing

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Learning the C language 3. The Nuts and Bolts
of C (4) 10 September 2008
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3.3 Expressions, Statements, and Blocks
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A Typical Program
include ltiostreamgt int abc (...) ...
return ... int cde (...) ... return
... int main() ... return 0
function
statements
function
function
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Statements

• A C program comprises a number of functions.
• A function comprises a number of statements.
• A statement can be as simple as
• Can be as complicated as
• A statement must end with a semicolon
• In a statement, space carries no information.

x a b
if (choice Sunday choice Saturday) cout
ltlt "\nYou're already off on weekends!\n"
x a b
?
x a b
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Expressions

• A statement comprises one or many expressions.
• Anything that returns a value is an expression.
• Examples of expressions
• 3.2 // Returns the value 3.2
• studentPerClass // Returns a constant, say 87
• x a b // Here, two expressions
• // Return a b and return the value of a
  variable x
• Since x a b is an expression (i.e. return a
  value) , it can certainly be assigned to another
  variable.
• For example,
• y x a b // assign y to the value of x
  which is
• // equal to the sum of a and b

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Operators

• An expression often comprises one of more
  operators.
• The assignment operator '' assigns a value to a
  variable or constant, e.g. x 39
• Several mathematical operators are provided by
  C.
• Let a be 3, b be 4 and x is declared as an
  integer,

Operators Meaning Add - Subtract
Multiply / Divide modulus
Examples x a b // x 7 x a - b // x
-1 x a b // x 12 x a / b // x 0
(why?) x a b // x 3 (why?)
3 modulo 4 is 3
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Integer and Floating Point Divisions
include ltiostreamgt using namespace std void
intDiv(int x, int y) int z x/y cout ltlt "z
" ltlt z ltlt endl void floatDiv(int x, int
y) float a (float)x // old style float b
static_castltfloatgt(y) // ANSI style float c
a/b cout ltlt "c " ltlt c ltlt endl int
main() int x 5, y 3 intDiv(x,y) floatDiv
(x,y) return 0
x, y of main() are not x, y of intDiv(int, int)
Casting Ask the compiler to temporarily consider
x as a floating point no., i.e. 5.0 in this case.
Only give integer division result, i.e. 1
Give floating point division result, i.e. 1.66...
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Shorthand of Expressions

• For some commonly used expressions, there are
  some shorthands.
• c c 1 ? c 1 ? c ? c
  //increment
• c c - 1 ? c - 1 ? c-- ? --c
  //decrement
• c c 2 ? c 2
• c c - 3 ? c - 3
• c c 4 ? c 4 // there is no c or
  c//,
• c c / 5 ? c / 5 // since it is
  meaningless
• Let c be an integer with value 5. Note that
• a c // a 5, c 6 since a c first and
  then c
• a c // a 6, c 6 since c first and
  then a c

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Precedence and Parentheses

• Mathematical operations are basically performed
  from left to right.
• It follows the normal mathematical precedence
  that multiplication / division first and addition
  / subtraction next.
• Hence
• To change the precedence, we can use parentheses.
• Parentheses can be nested as in normal
  arithmetic.

x 5 3 8 // x 29 since we evaluate 3
8 first
x (5 3) 8 // x 64 since we evaluate 5
3 first
x 5 ((3 2) 3 2) // x 5 (5 6)
55
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Exercise 3.3a
include ltiostreamgt int main() int myAge
39 // initialize two integers int
yourAge 39 cout ltlt "I am " ltlt myAge ltlt "
years old.\n" cout ltlt "You are " ltlt yourAge
ltlt " years old\n" myAge //
postfix increment yourAge // prefix
increment cout ltlt "One year passes...\n"
cout ltlt "I am " ltlt myAge ltlt " years old.\n"
cout ltlt "You are " ltlt yourAge ltlt " years
old\n" cout ltlt "Another year passes\n"
cout ltlt "I am " ltlt myAge ltlt " years old.\n"
cout ltlt "You are " ltlt yourAge ltlt " years
old\n" cout ltlt "Let's print it again.\n"
cout ltlt "I am " ltlt myAge ltlt " years old.\n"
cout ltlt "You are " ltlt yourAge ltlt " years
old\n" return 0
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Relational Operators

• Besides arithmetic operations, we can perform
  relational operations with C.
• A number of relational operators are defined in
  C.
• Each relational operator returns a bool result
  (true or false).
• In C, zero is considered false, and all other
  values are considered true.
• True is usually represented by 1.

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Relational Operators
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Applications of Relational Operators

• Relational operators are often used with if
  statement.
• The if statement provides branching of the
  program execution depending on the conditions.
• int bigNumber 10, smallNumber 5
• bool bigger bigNumber gt smallNumber //bigger
  true
• if (bigger)
• doSomeThing()

Or you can simply write if (bigNumber gt
smallNumber) doSomeThing()
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Logical Operators

• Logical operators do logical operations for bool
  variables.
• Each logical operation returns a bool result
  (true or false).

Operators Meaning AND OR ! NOT
Examples expression1 expression2 expression1
expression2 !expression
int bigNum 10, smallNum 5 if (bigNum lt 10
smallNum gt 0) doSomeThing()
Will doSomeThing() be called???
NO
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int bigNum 10, smallNum 5 if ((bigNum lt 10
smallNum gt 0) bigNum gt smallNum) doSomeT
hing()
F
T
Will doSomeThing() be called???
YES
int bigNum 10, smallNum 5 if (!(bigNum gt
smallNum)) doSomeThing()
Will doSomeThing() be called???
NO
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Exercise 3.3b
The following program asks user to enter 3
numbers. If the sum of the first two is equal to
the last one, a message is printed to the
console. a. Build the project and note the
result. Does it perform correctly? b. If not,
fix the problem and re-build the program.
include ltiostreamgt using namespace std int
main() int a, b, c cout ltlt "Enter 3
numbers \n" cin gtgt a cin gtgt b cin gtgt
c if (c (ab)) cout ltlt "c ab\n"
return 0
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Acknowledgment

• The slides are based on the set developed by Dr.
  Frank Leung (EIE).
• Teach Yourself C in 21 Days, Second Edition
  (http//newdata.box.sk/bx/c/)

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Reading

• Read Hours 4-5 in 24 hours