Repetition

LoopsAllows the same set of

instructions to be used over and over again

Starts with the keyword loop and ends with end loop. This will create an infinite loop and you have to press the stop button in the execution window to exit.

Loopexample1.t% The "ManyCircleAreas" program% Computes the areas of circlesvar radius, area : realconst pi :real := 3.14159loop

put "Enter radius " ..get radiusarea := pi * radius ** 2put "Area is ", area

end loop

Conditional Loops

You can stop a loop by putting a condition in your loop. For example, you can make the first example exit the loop when a negative number is entered for the radius. This signal is called a sentinel.. This is done using the exit when command.

Conditional OperatorsThe operators that can be used with the exit

when command are:> value “Greater than value”< value “Less than value”= value “equal value”>= value “Greater than or equal to value”<= value “Less than or equal to value”not= value “not equal to a value”

Also called BOOLEAN Operator. Returns a value of either True or False.

Loopexample2.t% The "ManyCircleAreas2" program% Compute circle areas until you enter a negative

radiusvar radius, area : realconst pi :real := 3.14159put "Enter a negative radius to stop execution"loop

put "Enter radius " ..get radiusexit when radius < 0area := pi * radius ** 2put "Area is ", area

end loopput "That's all folks"

The condition exit when radius < 0, exits the loop when a negative number is entered in for a radius.

Change the condition so the loop exits when the radius is equal to -1.

Comparing StringsWhen comparing strings, computers use

their ASCII value. for example the character "A" is 65, "B"

is 66, "C" is 67, and so on. Lower case letters have different values: "a" is 97, "b“ is 98, etc. This means that the condition"A" < "B"is true and also that"a" < "B"is false.

Loopexample3.t% The "ComputeAverage" program% Compute the average of a series of marks% Give average to the nearest integervar mark : intvar count, sum : int := 0const sentinel :real := – 1put "Enter a series of marks"put "End with ", sentinelloop

get markexit when mark = sentinelcount := count + 1sum := sum + mark

end loopput "Average mark is ", round (sum / count )

Notice:We initialized the variable sum

and count to 0. Notice the command round() will

round an answer to an operation in the brackets.

Another variable called average should be declared of type real to store the average calculation.

average := round(sum/count)Also… try…..average := sum div count

Loopexample4.t% The "Obey" program% Read in a series of words% until the word "stop" is readvar word : stringput "Enter a series of words, one to a line"put "If you want to stop say so"loop

get wordexit when word = "stop"

end loopput "This is the end"

Counted LoopsWe have looked at conditional and

infinite loops.Counted loops allows you to specify

how many times you want the loop to run.

CODE:for count : startnumber ..

endnumber {Body} end for

Loopexample5.t% The "ComputeAverages" program% Reads marks and computes averagevar mark : intvar sum : int := 0put "Enter marks"for count : 1 .. 5

put countget marksum := sum + mark

end forput "Average is ", round (sum / 5)

Good programming practice

From the previous example, it is good programming practice to use a variable instead of the number “5”.

We could define a constant:◦const numMarks : real := 5

And then change the following lines:◦for count 1 .. numMarks◦put "Average is ", round (sum /

numMarks)

Loopexample6.t

var start, stop : intput "Enter the initial and final values for

the loop: " ..get start, stopfor i : start .. stop

put iend for

Counting by MultiplesLoopexample7.t

%Starts at 2 and goes up by 2 until it reaches 10

for count : 2 .. 10 by 2 put countend for%Starts at 1 and goes up by 5 until it

reaches 10for count : 1 .. 10 by 5 put countend for

QuestionsPg. 138/500 on the IPT.pdfDo questions #1-6

LOOK AT THE EXAMPLES FROM THIS NOTE WHEN CODING YOUR PROGRAMS.

REMEMBER TO COMMENT!!!