Control Statements

1
Chapter 4

• Control Statements

2
Revisit Operators

• -- used for raising to a power
• Negative exponent means use reciprocal, i.e. 3-2
  1/32
• / -- used with integer produces an integer
• 5/3 2
• Rem used to find out remainder in integer
  division
• 5 Rem 3 2

3
General Formatting

• New_line
• Moves cursor to the next line down
• New_page
• Moves cursor to the top of the next page
• Set_col(20)
• Moves cursor to column 20 on the present line
• If already past column 20, will go to next line
  and column 20

4
Formatting Integers

• Put(Num2)
• No width given so gives enough space to print the
  largest integer possible!!
• Put(Num2, widthgt2)
• Put(Num2, 2)
• If width is too small will use as much space as
  needed
• Alligns number on the right of the spaces

5
Formatting Floats

• Put(Salary)
• Defaults to exponential form, e.g. 3.45E2
• Put(Salary, foregt3,aftgt2, expgt0)
• 345.00
• Put(Salary,3,2,0)

6
Try these Remember order of operations!

• 6 5 2 / 8 4 rem 3
• 16 2.0
• 3.0 16.0 / float(3) 2
• 15 / integer(3.6)

7
Three Fundamental Control Structures

• Sequence
• Selection
• Iteration (Repetition)

8
The Assignment Statement

• Only one variable on left side of
• Right side of is evaluated then assigned to
  the variable on leftExamples
• My_Salary 3250.0
• Commission 0.125 Sales
• Name Kincade, Thomas
• FirstName(1..6) Name(10..15)

9
Sequence

• Put_line(Enter two integers)
• Get(Num1)
• Get(Num2)
• Sum Num1Num2
• Put(The sum is )
• Put(sum)

10
Selection(Simple If then)

• If Num1 lt 10 and Num2 lt 10 Then
• Put(The sum is less than 20)
• End If -- simple If statement
• If Age1 lt 12 or Age2 lt 12 Then
• Put(At least one is a child)
• End If

11
Selection(If then else)

• If Age lt 18 then
• Put(Person cannot vote)
• Else
• Put(Person can vote)
• End if

12
Selection(use of Elsif categorizing ages)

• If Age lt 3 Then
• Put(toddler)
• Tod_count Tod_count 1
• Elsif Age lt 12 then
• Put(child)
• Child_count Child_count 1
• Elsif Age lt 20 then
• Put(teen)
• Teen_count Teen_count 1
• Else
• Put(Adult)
• Adult_count Adult_count 1
• End If

13
Selection(Find smallest)

• Put_line(Enter 3 different integers)
• Get(A) Get(B) Get(C)
• If AltB and BltC then
• put(A) put( is the smallest)
• Elsif BltA and B lt C then
• put(B) put( is the smallest)
• Else
• put(C) put( is the smallest)
• End if

14
Example Nested If

• Lets write an algorithm to tell how many roots
  of the equations exist
• Remember quadratic equation
• Ax2 Bx C 0
• Assume A, B, C are given to the program
• First rule out a constant or linear equation (A
  0 and B 0)
• Then (if quadratic) begin checking the
  determinant (B2 4AC)

15
Code

• If A / 0 And B / 0 Then -- quadratic
• If B2 4 A C gt 0 Then
• Put(There are 2 real roots)
• ElsIf B2 4 A C 0 Then
• Put(There is only one root)
• Else
• If B2 4 A C lt 0 Then
• Put(There are 2 complex number roots)
• End If
• Else
• Put(This is not a quadratic equation)
• End If

16
Lab Problem

• If sides make a triangle Then
• If three sides are equal then
• Display the 3 lengths equilateral
• elseif two sides are equal then
• Display the 3 lengths isosceles
• else
• Display the 3 lengths scalene
• end nested if
• Else
• Display not a triangle
• End the outer if

17
Case statement
Must be discrete expression (not float!)

• Case selector is
• When choice1 gt
• Statements to execute
• When choice2 gt
• Statements to execute
• When others gt
• Statements to execute
• End case

Use when there are other possibilities!
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Example

• Case month_num is
• When 1..2 12 gt
• Put(Winter)
• When 3..5 gt
• Put(Spring)
• When 91011
• Put(Autumn)
• When others gt
• Put(Error in month number)
• End case

19
Another Example

• Get(ch)
• Case ch is
• When a..z A..Z gt
• Alpha_count alpha_count 1
• Put(alphabet character)
• When 0..9 gt
• Digit_count digit_count 1
• Put(digit character)
• When others gt
• Other_count other_count 1
• Put(other character)
• End case

20
Iteration

• Repetition in Ada

21
Looping

• Infinite loop
• Loop
• Put(hello there!)
• End loop
• Execute a fixed number of times
• For J in 1..10 loop
• Put(hello there!)
• End loop

For J in reverse 1..10 loop Put(J) End loop
22
Looping
Do not declare this variable!

• Execute a fixed number of times
• For J in 1..10 loop
• Put(hello there!)
• End loop
• For ch in character range a..z loop
• Put(ch)
• End loop

Note book is incorrect!
23
Looping

• Executed until a certain condition is met
• While boolean expression loop
• statements
• End loop
• While x / -1 loop
• Put(x)New_line
• Put(Enter an integer use 1 to stop )
• Get(x)
• End loop

24
Looping

• Using exit when statement
• Must be within the loop
• Loop
• Put(x)New_line
• Put(Enter an integer use 1 to stop )
• Get(x)
• Exit when x -1
• End loop

25
Looping

• Interactive loop
• Initialize in declaration, e.g.
• resp character y
• Begin
• Loop
• Put(Enter an integer)
• Get(N)
• Put(Do you want to continue -- y or n)
• Get(resp)
• Exit When resp n or resp N
• End Loop

26
Another Interactive loop

• Initialize in declaration, e.g.
• resp character y
• Begin
• While resp / n and resp / N Loop
• Put(Enter an integer)
• Get(N)
• Put(Do you want to continue -- y or n)
• Get(resp)
• End Loop

27
Finding an Average What all do we need??

• Counter (adds same number each time)
• Accumulator (summing variable adds a different
  value to an accumulating sum)
• Average is found by dividing Accumulator by
  Counter ---how accurate do you want?? (probably
  will want float!)

28
Example finding the average age of the class

• Count 0
• Sum 0
• Resp y
• Loop
• Get(Age)
• Count Count 1
• Sum Sum Age
• Put(any more ages? Y or N )
• Get(Resp)
• Exit when resp / Y or resp / y
• End loop
• Now I can find the average by dividing Sum by
  Count!!!

I could initialize these in declaration!