[IGCS] Counting Loop

[IGCS] Counting Loop

There are mainly two types of loops

• Conditional loops - Number of time is indefinite

• Counting loops - Loop with a definite number of times

Open Ended

What are the two types of condition loops?

Counting

counter <- 0

WHILE counter < 10 DO

⠀# do something....

⠀counter <- counter + 1

ENDWHILE

For loop

# The previous slide's counting algorithm can be rewrite using for loop:

FOR counter <- 0 to 9 DO

⠀# Do something

NEXT counter

Multiple Choice

If we write:

FOR counter <- 0 to 5 DO

PRINT counter

NEXT counter

What will be the last number to print?

• 0

• 4

• 5

• 6

FOR [count_var] <- [start] to [stop] DO

• count_var the variable that used as counter, usually we use counter or i, j, k to name counter

• start: the value that the count_var is initialized with. In other word, count_var = start when the loop is first executed

• stop: the loop ends when counter reaches stop value.

• i.e. count_var = stop when the last time the loop run

Python for loop is a bit different

# In Python

for counter in range(0, 10):

⠀print(counter)

# implies that the counter is counting from 0 to 9 (not including 10)

# so the above code will print from 0 - 9 only

Open Ended

Describe what is the following program produce:

FOR i <- 10 to 1 DO

⠀PRINT i

NEXT i

For the previous program, it will be:

for i in range(10, 0, -1):

⠀print(i)

# when coding in Python

Multiple Choice

What is the range of the value (inclusive) if we write:

range(5)

• 1..5

• 0..5

• 0..4

• 1..4

Multiple Choice

What is the range of the value (inclusive) if we write:

range(0, 5)

• 1..5

• 0..5

• 0..4

• 1..4

Multiple Choice

What will be the sequence of number generated if we write:

range(1, 5, 1)

• 1 2 3 4 5

• 0 1 2 3 4 5

• 0 1 2 3

• 1 2 3 4

Multiple Choice

What will be the sequence of number generated if we write:

range(0, 5, 2)

• 0 1 2 3 4

• 0 1 2 3 4 5

• 0 2 4

• 0 2 4 6

Multiple Choice

What will be the sequence of number generated if we write:

range(3, 0, -1)

• 0 1 2 3

• 0 1 2

• 3 2 1 0

• 3 2 1

Open Ended

Write the range() function to generate 0-5 (inclusive)

Open Ended

Write the range() function to generate even numbers from 0-10 (inclusive)

Multiple Select

** Which of the following program(s) print first 5 odd numbers?

• for i in range(10):

  print(i*2 + 1)

• for i in range(1, 9, 2):

  print(i)

• for i in range(1, 11, 2):

  print (i)

• for i in range(1, 10, 2):

  print(i)

• for i in range(0,5,2):

  print(i*2 + 1)

Summary

• Use For-loop when the number of times is definite

• The counter range can be customized by specifying: start, end and interval