Chapter 4

Control Statements

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

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

Formatting Integers Put(Num2);

No width given so gives enough space to print the largest integer possible!!

Put(Num2, width=>2); Put(Num2, 2);

If width is too small will use as much space as needed

Alligns number on the right of the spaces

Formatting Floats Put(Salary);

Defaults to exponential form, e.g. 3.45E2

Put(Salary, fore=>3,aft=>2, exp=>0) 345.00

Put(Salary,3,2,0)

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)

Three Fundamental Control Structures Sequence

Selection

Iteration (Repetition)

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)

Sequence

Put_line(“Enter two integers”);Get(Num1);Get(Num2);Sum := Num1+Num2Put(“The sum is ”);Put(sum);

Selection(Simple If then)

If Num1 < 10 and Num2 < 10 Then Put(“The sum is less than 20”);End If; -- simple If statement

If Age1 <= 12 or Age2 <= 12 Then Put(“At least one is a child”);End If;

Selection(If then else)

If Age < 18 then Put(“Person cannot vote”);Else Put(“Person can vote”);End if;

Selection(use of Elsif – categorizing ages)

If Age < 3 Then Put(“toddler”); Tod_count := Tod_count + 1;Elsif Age < 12 then Put(“child”); Child_count := Child_count + 1;Elsif Age < 20 then Put(“teen”); Teen_count := Teen_count + 1;Else Put(“Adult”); Adult_count := Adult_count + 1;End If;

Selection(Find smallest)

Put_line(“Enter 3 different integers”);

Get(A); Get(B); Get(C);If A<B and B<C then put(A); put(“ is the smallest”);Elsif B<A and B < C then put(B); put(“ is the smallest”);Else put(C); put(“ is the smallest”);End if;

Example Nested If Let’s 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)

CodeIf A /= 0 And B /= 0 Then -- quadratic If B2 – 4 * A * C > 0 Then

Put(“There are 2 real roots”);

ElsIf B2 – 4 * A * C = 0 ThenPut(“There is only one root”);

ElseIf B2 – 4 * A * C < 0 ThenPut(“There are 2 complex number roots”);

End If;Else

Put(“This is not a quadratic equation”);

End If;

Lab ProblemIf 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 ifElse Display “not a triangle”End the outer if

Case statement

Case selector isWhen choice1 =>

Statements to execute

When choice2 =>Statements to execute

When others =>Statements to execute

End case;

Must be discrete expression (not float!)

Use when there are other possibilities!

Example:Case month_num is

When 1..2 | 12 =>Put(“Winter”);

When 3..5 =>Put(“Spring”);

When 9|10|11Put(“Autumn”);

When others =>Put(“Error in month number”);

End case;

Another Example:Get(ch);Case ch is

When ‘a’..’z’ | ‘A’..’Z’ =>Alpha_count := alpha_count + 1;Put(“alphabet character”);

When ‘0’..’9’ =>Digit_count := digit_count + 1;Put(“digit character”);

When others =>Other_count := other_count + 1;Put(“other character”);

End case;

Iteration

Repetition in Ada

Looping

1. Infinite loopLoop

Put(“hello there!”);

End loop;

2. Execute a fixed number of timesFor J in 1..10 loop

Put(“hello there!”);

End loop;

For J in reverse 1..10 loop

Put(J);

End loop;

Looping

2. Execute a fixed number of timesFor 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!

Do not declare this variable!

Looping

3. Executed until a certain condition is met

While boolean expression loopstatements;

End loop;While x /= -1 loop

Put(x);New_line;Put(“Enter an integer – use –1 to stop ”);Get(x);

End loop;

Looping Using exit when statement

Must be within the loopLoop

Put(x);New_line;Put(“Enter an integer – use –1 to stop ”);Get(x);Exit when x = -1

End loop;

Looping Interactive loop

Initialize in declaration, e.g.

resp : character := ‘y’;BeginLoop

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;

Another Interactive loop Initialize in declaration, e.g. resp : character = ‘y’;BeginWhile 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;

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!)

Example: finding the average age of the classCount := 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!