Python Loops | while Loop, for Loop, range(), break, continue and pass

In many situations, a programmer needs to execute the same set of statements multiple times. Writing the same code repeatedly makes the program lengthy, difficult to understand, and harder to maintain. Python provides loops to solve this problem. A loop repeatedly executes a block of statements until a specified condition becomes false or a sequence is completely processed.

Loops are one of the most powerful features of Python and are widely used in applications such as displaying reports, processing records, generating tables, validating user input, and performing repetitive calculations.

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Learning Outcomes

After studying this chapter, you will be able to:

• Understand the concept of looping.
• Differentiate between while and for loops.
• Use the range() function.
• Write programs using loops.
• Understand nested loops.
• Control loop execution using break, continue, and pass.

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What is a Loop?

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Why Do We Need Loops?

Suppose you want to display the message "Welcome to Python" ten times.

Without a loop:

print("Welcome to Python")
print("Welcome to Python")
print("Welcome to Python")
print("Welcome to Python")
print("Welcome to Python")
print("Welcome to Python")
print("Welcome to Python")
print("Welcome to Python")
print("Welcome to Python")
print("Welcome to Python")

Using a loop:

for i in range(10):
    print("Welcome to Python")

Using loops makes the program shorter, easier to understand, and easier to maintain.

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Advantages of Loops

• Reduce the amount of code.
• Avoid repetition.
• Improve readability.
• Save programming time.
• Make programs easier to modify.

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Types of Loops in Python

Loop	Used When
while	Number of iterations is not known in advance.
for	Number of iterations or sequence is known.

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The while Loop

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Syntax of while Loop

while condition:
    statement(s)

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Flowchart of while Loop

        Condition
            |
      +-----+------+
      |            |
    True        False
      |
 Execute Block
      |
 Update Condition
      |
      +------------+

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Example 1: Print Numbers from 1 to 5

count = 1

while count <= 5:
    print(count)
    count = count + 1

Output

1
2
3
4
5

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Working of the Program

Iteration	Value of count	Condition	Output
1	1	True	1
2	2	True	2
3	3	True	3
4	4	True	4
5	5	True	5
6	6	False	Loop Stops

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Example 2: Multiplication Table

num = int(input("Enter a number: "))
i = 1

while i <= 10:
    print(num, "x", i, "=", num*i)
    i = i + 1

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Infinite Loop

Example

while True:
    print("Python")

Note: Avoid creating infinite loops unless they are intentionally required.

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The for Loop

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Syntax of for Loop

for variable in sequence:
    statement(s)

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Flowchart of for Loop

Start
  |
Next Item
  |
Execute Block
  |
More Items?
  |
Yes --------+
 |
No
 |
End

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Example 3: Print Numbers from 1 to 5

for i in range(1,6):
    print(i)

Output

1
2
3
4
5

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Example 4: Display Student Names

students = ["Aarav","Diya","Riya","Kabir"]

for name in students:
    print(name)

Output

Aarav
Diya
Riya
Kabir

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Example 5: Iterate Through a String

for ch in "Python":
    print(ch)

Output

P
y
t
h
o
n

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The range() Function

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Forms of range()

Function	Description
range(stop)	Generates numbers from 0 to stop − 1.
range(start, stop)	Generates numbers from start to stop − 1.
range(start, stop, step)	Generates numbers with the specified step value.

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Example 6: range(stop)

for i in range(5):
    print(i)

Output

0
1
2
3
4

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Example 7: range(start, stop)

for i in range(3,8):
    print(i)

Output

3
4
5
6
7

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Example 8: range(start, stop, step)

for i in range(2,21,2):
    print(i)

Output

2
4
6
8
10
12
14
16
18
20

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Nested Loops

A loop placed inside another loop is known as a nested loop. The inner loop executes completely for every iteration of the outer loop.

Example

for i in range(1,4):
    for j in range(1,4):
        print(i,j)

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Loop Control Statements

Sometimes, while executing a loop, we may need to stop the loop immediately, skip certain iterations, or keep a placeholder for future code. Python provides three loop control statements for this purpose:

• break
• continue
• pass

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The break Statement

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Syntax of break

for variable in sequence:
    if condition:
        break
    statement(s)

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Flowchart of break Statement

       Start Loop
           |
     Condition True?
      /           \
    Yes           No
     |             |
   break      Execute Block
     |             |
     +-------> Exit Loop

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Example 1: Stop the Loop at 5

for i in range(1,11):
    if i == 5:
        break
    print(i)

Output

1
2
3
4

When i becomes 5, the break statement is executed, and the loop terminates immediately.

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Real-Life Example

An ATM machine allows three attempts to enter the correct PIN. Once the correct PIN is entered, the verification loop stops immediately using the break statement.

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The continue Statement

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Syntax of continue

for variable in sequence:
    if condition:
        continue
    statement(s)

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Flowchart of continue Statement

      Start Loop
          |
    Condition True?
      /         \
    Yes         No
     |           |
continue    Execute Block
     |           |
     +-------> Next Iteration

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Example 2: Skip Number 5

for i in range(1,11):
    if i == 5:
        continue
    print(i)

Output

1
2
3
4
6
7
8
9
10

The value 5 is skipped, but the loop continues with the remaining iterations.

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Real-Life Example

A school management system processes the attendance of all students. If a student's record is incomplete, the system skips that record using continue and processes the next student's data.

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The pass Statement

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Syntax of pass

if condition:
    pass

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Example 3: Using pass

for i in range(1,6):
    if i == 3:
        pass
    print(i)

Output

1
2
3
4
5

The pass statement performs no operation. The program continues executing normally.

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Why is pass Useful?

• Acts as a placeholder during program development.
• Prevents syntax errors when a code block is intentionally left empty.
• Allows developers to write incomplete programs without causing execution errors.

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Comparison of Loop Control Statements

Statement	Purpose	Effect on Loop
break	Terminates the loop immediately.	Loop stops completely.
continue	Skips the current iteration.	Loop continues with the next iteration.
pass	Does nothing.	Loop executes normally.

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Comparison of while Loop and for Loop

while Loop	for Loop
Used when the number of iterations is not known.	Used when the number of iterations is known.
Condition-controlled loop.	Sequence-controlled loop.
Requires manual initialization and updation.	Initialization and iteration are handled automatically.
Suitable for validation and menu-driven programs.	Suitable for traversing sequences such as strings, lists, and ranges.

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Common Programming Errors

Mistake	Correct Practice
Forgetting to update the loop variable in a while loop.	Always update the loop variable to avoid infinite loops.
Using break instead of continue.	Use break to terminate the loop and continue to skip an iteration.
Incorrect indentation inside the loop.	Maintain proper indentation for all loop statements.
Using an incorrect range() value.	Remember that the stop value is not included.
Creating an infinite loop accidentally.	Ensure that the loop condition eventually becomes false.

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Interview Corner

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Quick Revision

Concept	Remember
Loop	Repeats a block of statements.
while	Condition-controlled loop.
for	Sequence-controlled loop.
range()	Generates a sequence of numbers.
break	Terminates the loop immediately.
continue	Skips the current iteration.
pass	Null statement used as a placeholder.
Nested Loop	A loop inside another loop.

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Important Points to Remember

• Loops help avoid writing repetitive code.
• The while loop is used when the number of iterations is not known in advance.
• The for loop is generally used to iterate over a sequence.
• The range() function generates a sequence of numbers.
• The stop value in range() is always excluded.
• break terminates the loop immediately.
• continue skips the current iteration.
• pass performs no action and is mainly used as a placeholder.

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CBSE Exam Tips

• Understand the difference between while and for loops.
• Practice all three forms of the range() function.
• Learn the behavior of break, continue, and pass with examples.
• Trace loop execution step by step to determine the output.
• Pay attention to indentation while writing loop programs.
• Practice writing programs for tables, factorials, sums, and pattern generation using loops.

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Summary

Loops are essential control structures that allow a program to execute a block of statements repeatedly. Python provides the while loop for condition-based repetition and the for loop for iterating over sequences. The range() function simplifies numeric iteration, while the break, continue, and pass statements provide additional control over loop execution. A strong understanding of loops enables students to write efficient, concise, and logical programs, making them an indispensable part of Python programming.