Procedural Programming

1
Procedural Programming Structured Programming

• Control structures
• Sequence the default
• Conditional in these slides
• Looping in other slides

2
Procedural Programming

• OOP vs. PP (Procedural ) paradigm ?
• - - - - - - - - - - - - - - - - - - - - - - - - -
  - - - - - - - -
• OOP class packaging of
• 1) storage for attributes of objects of this
  class type
• 2) behaviors (methods) of objects of this class
  type
• Methods ( constructors get/set accessors)
• procedural programming

3
Procedural Programming

• Procedure (algorithm)
• steps to take to solve a problem
• 1st . . .
• 2nd . . .
• . . .
• last . . .

4
Program/method consists of

• 1) Action statements to execute
• operate on data
• Arithmetic (on numeric types) - /
• Concatenate (string types)
• move data around
• in memory (assignment)
• memory to/from screen/keyboard (or a file, )
• WriteLine, ReadLine

5

• 2) statements to Control the order in
  which actions execute
• transfer control
• To next statement (in physical sequence) ( the
  default)
• Possibly skip an action(s), based on a condition
• Choose next action from several, based on a
  condition
• Loop around do actions again
• A fixed number of times
• A variable number of times, based on if condition
  is true or false
• Call a method (a procedure) return here when
  its done
• Method itself does actions may transfer control
  further
• Go to some statement dont return when done

6
3 control structures

• Structured Programming
• Sequence (the default)
• Selection (conditional execution)
• Repetition (looping)

7
Sequence
1 statement after another, in order (1st,
2nd, 3rd, ...) start at the top continue til
you hit the end
8
Selection (if-then-else)
DECISION determine which of 2 paths to follow
(1 or more statements in each path)
9
Loop
Repeat 1 statements based on whether specified
condition is true or false also a for loop
UNTIL there are no more students
WHILE there are more students
10
Combine the 3 structures

• Stack them
• or
• Nest them

11
Selection options (in C)

• selection guard, decision, conditional
• Single selection if
• Double selection if ... else
• Multiple selection
• switch (case in some languages)
• or
• if else if else if else

12
Repetition options (in C)

• Event-controlled
• (loop as long as condition is true)
• while (pre test)
• do . . . while (post test)
• Count-controlled
• (loop a specified number of times)
• for
• foreach

13
Selection Control Structure

• if, if/else
• conditions

14
Plain ifs (3 variations)

• if (condition)
• action
• ------------------
• if (condition)
• action

• if (condition)
• action1
• . . .
• actionN

15
if else (3 variations)

• if (condition)
• action1
• else
• action2
• ------------------
• if (condition)
• action1
• else
• action2

• if (condition)
• action1a
• . . .
• action9a
• else
• action1b
• . . .
• action9b

16
Each action could be

• A simple action
• Assignment state
• with arithmetic expression or function call
• I/O
• Call to another method
• Another selection statement if or if. .
  .else or switch
• A while or do while or for loop
• do absolutely NOTHING

17
Conditions

• Comparison (equality, relational) operators
• ! lt gt lt gt
• NOTE compare for equality
• is the assignment operator
• Compare 2 things (2 operands) which are
• - variables, constants, arithmetic expressions,
• returned values from a method call,
• . . .

18
Conditions are true or false

• (a lt b)
• (a ! 25)
• ( (a 2 3) lt ( (b - 4) 3) )
• ( (Math.PI r r) lt maxSize )
• NOTE need ( ) around whole condition

19
Logic operators in conditions

• (and) (or) !
  (not)
• ( !(a 25) ) same as (a ! 25)
• ( (a lt b) (c lt d) )
• ( (a 3) (c 1) )
• Note use Truth tables

20
Order of precedence ?

• ( (a b) (c gt -14) ) typical
• (a b) (c gt -14) WRONG
• ( a b c gt -14 ) OK
• students with gpas gt 3.0 from Michigan and
  Ohio? NO
• (gpa gt 3.0 state MI state
  OH)
• ( (gender F) (age gt 21)
• (gpa gt 2.5) (!(major CS)) )

21
Order of precedence of operators

• Unary operators - !
• Arithmetic operators /
• -
• Relational operators lt gt lt gt
• equality operators !
• Logic operators AND
• OR
• Assignment operator

22
Actions e.g.,

• total total 1
• counter
• Console.WriteLine(blah blah)
• n Convert.ToInt32
• ( Console.ReadLine() )
• if (state MI)
• . . .
• if (state MI)
• . . .
• . . .
• else
• . . .
• // meaning do NOTHING !!!

23
Empty block of actions

• UNUSUAL (bad?)
• if (a lt b)
• Console.Write(hi)
• // empty if so Write will ALWAYS happens
• COMMON
• if (a lt b) // NO here
• Console.Write(hi)
• // empty if so Write MAY happen

24
Nested if/else

• if (a 4) // note formatting
• if (b 5)
• answer 1
• else
• answer 2
• else
• if (b 5)
• answer 3
• else
• answer 4
• // trace this code !

25
Empty statement

• if (a 4)
• if (b 5)
• // OK, do nothing here
• else
• answer 2
• else
• if (b 5)
• answer 3
• else
• answer 4

26
Dangling else ?

• if (a 4)
• if (b 5)
• answer 1
• // WRONG ?
• else // this else paired with if (b5)
• if (b 5)
• answer 3
• else
• answer 4
• // NOTE compiler ignores formatting and
  does what instructions actually say

27
Prior example actually says

• if (a 4)
• if (b 5)
• answer 1
• else // so b ! 5 here
• if (b 5)
• answer 3
• else
• answer 4

28
Dangling else - the FIX

• if (a 4)
• if (b 5)
• answer 1
• else
• if (b 5)
• answer 3
• else
• answer 4

29
Nested if/else if/else . . .

• NOT TYPICAL FORMATTING
• if (total gt 90)
• Console.WriteLine(A)
• else
• if (total gt 80)
• Console.WriteLine(B)
• else
• if (total gt 70)
• Console.WriteLine(C)
• else
• if (total gt 60)
• Console.WriteLine(D)
• else
• Console.WriteLine(E)

30
Nested generally written as

• if (total gt 90)
• Console.WriteLine(A)
• else if (total gt 80)
• Console.WriteLine(B)
• else if (total gt 70)
• Console.WriteLine(C)
• else if (total gt 60)
• Console.WriteLine(D)
• else
• Console.WriteLine(E)

31
Nested if/elsesvs. Stacked ifs

• NESTED if/elses
• control goes to ONLY 1 category (condition)
• ONLY 1 set of actions is done (or none)
• used for these situations
• mutually exclusive categories - state example
• use 1st category that applies - grades example
• STACKED ifs
• control goes to ALL conditions)
• ALL sets of actions MIGHT be done
• used for these situations
• use all categories that apply - cummulative
  bonus example

32
Nested if/elses

• control goes to ONLY 1 category
• the 1st one that applies
• and none of the rest of the else if s
• so the ORDER may be important
• NO for mutually exclusive categories - state
  example
• YES for use 1st category that applies - grades
  example
• if (state MI)
• . . .
• else if (state IN)
• . . .
• NOTE final else is optional

33
Stacked ifs

• bonus 0
• if (attendance gt 25)
• bonus bonus 5
• if (labPoints gt 900)
• bonus bonus 35

34
Stacked - WRONG

• if (total gt 90)
• Console.WriteLine(A)
• if (total gt 80)
• Console.WriteLine(B)
• if (total gt 70)
• Console.WriteLine(C)
• if (total gt 60)
• Console.WriteLine(D)
• Console.WriteLine(E)

35
if/else in a box

• Special conditional operator ?
• Console.Write (age gt 21 ? OK NO)
• 1st Condition ? TRUE or FALSE
• 2nd VALUE of parameter when condition is TRUE
• 3rd VALUE of parameter when condition is FALSE

36
Switch statement

• Equivalent to nested if/else
• Later