7.13 Iteration (for and while) | Grade 9 New Curriculum Computer Science 2082

 

7.13 Iteration (for and while)

Iteration is the process of repeating a block of code multiple times until a specified condition is satisfied.

 

Types of iterations

·       for loop

·       while loop

 

For Loop

A for loop in Python is a control flow structure that allows to iterate over a sequence (like a list, tuple, string) or a range of numbers.

It is used when we know in advance how many times we want to execute a statement or a block of statements.

 

Syntax:

for variable in sequence:

    # Code to execute

 

Example:

# Iterating over a range of numbers from 0 to 4

for i in range(5):

    print(i)

 

Example:

#Using for loop to print “jump” five times

for x in range(5):

     print(“Jump!”)

 

Example:

# Iterating over a list

fruits = ["apple", "banana", "cherry"]

for fruit in fruits:

    print(fruit)

 

While Loop

“While loop” in Python is a control structure that allows to repeatedly execute a block of code as long as certain conditions remain true.

Syntax:

while condition:

    # Code to execute

 

Example:

# Using while loop to print numbers from 0 to 4

i = 0

while i < 5:

    print(i)

    i += 1  # Incrementing the value of i to avoid infinite loop

 

pass Statement

·       In Python, the pass keyword is a null operation or a no-operation statement.

·       It acts as a placeholder where some code is required but no action is necessary.

·       It is often used when a statement is required by Python syntax, but you don’t want to execute any code.

 

Syntax:

if condition:

    # Some code here

else:

    pass # Nothing happens in the “else” case

 

Example:

for i in range(5):

    if i == 2:

        pass  # Do nothing if i is 2

    else:

        print(i)

 

Output:

0

1

3

4

 

In this example, when i is equal to 2, the pass statement is executed, which does nothing, so the loop continues without printing 2.

 

 

 

 

continue Statement

·       In Python, the continue keyword is used in loops (such as for or while loops).

·       It is used to skip the rest of the code inside the loop for the current iteration and move on to the next iteration.

·       It allows us to bypass certain parts of the loop based on a condition without exiting the loop entirely.

 

Example:

 

for i in range(5):

    if i == 2:

        continue  # Skip the rest of the code when i is 2

    print(i)

 

Output:

 

0

1

3

4

 

Here, when i == 2, the continue statement skips the print(i) and moves to the next iteration of the loop, so 2 is not printed.

 

break Statement

·       In Python, the break keyword is used in loops (such as for or while loops) to exit the loop early, even if the loop’s condition hasn’t been fully satisfied.

·       It allows us to terminate the loop based on a certain condition.

 

Example:

 

for i in range(5):

    if i == 3:

        break  # Exit the loop when i is 3

    print(i)

 

Output:

 

0

1

2

 

In this case, when i == 3, the break statement causes the loop to terminate, and no further numbers are printed.