What Are Loops and Why Do We Need Them?
Loops are programming constructs that enable the execution of a block of code multiple times. They eliminate the need to write the same code over and over again, making programs more concise and efficient. Imagine having to print the numbers from 1 to 1000 or process each element in a large list manually – loops make these tasks manageable and less error-prone.
While Loop
The while loop is a type of loop that repeatedly executes a block of code as long as a specified condition is True. It's suitable for situations where you're uncertain about the exact number of iterations needed.
Syntax:
while condition:
# Code to be executed
Example:
count = 1
while count <= 5:
print("Count:", count)
count += 1
Output:
Count: 1
Count: 2
Count: 3
Count: 4
Count: 5
l. Using else Statement with While Loop:
num = 0
while num < 5:
print(num, "is less than 5")
num += 1
else:
print(num, "is not less than 5 anymore")
Output:
0 is less than 5
1 is less than 5
2 is less than 5
3 is less than 5
4 is less than 5
5 is not less than 5 anymore
ll. Infinite While Loop:
while True:
user_input = input("Enter 'q' to quit: ")
if user_input == 'q':
break
For Loop
The for loop is another essential construct in Python that iterates over a sequence (such as a list, tuple, string, or dictionary) and executes a block of code for each element in the sequence.
Syntax:
for element in sequence:
# Code to be executed
Examples:
l. Using For Loop with List:
fruits = ['apple', 'banana', 'orange']
for fruit in fruits:
print("I like", fruit)
Output:
I like apple
I like banana
I like orange
ll. Using For Loop with Tuple:
coordinates = [(1, 2), (3, 4), (5, 6)]
for x, y in coordinates:
print("x:", x, "y:", y)
Output:
x: 1 y: 2
x: 3 y: 4
x: 5 y: 6
lll. Using For Loop with String:
message = "Hello, Python"
for char in message:
print(char)
Output:
H
e
l
l
o
,
P
y
t
h
o
n
lV. Using For Loop with Dictionary:
student_scores = {'Alice': 85, 'Bob': 92, 'Eve': 78}
for name, score in student_scores.items():
print(name, "scored", score)
Output:
Alice scored 85
Bob scored 92
Eve scored 78
V. Using else Statement with For Loop:
numbers = [1, 2, 3, 4, 5]
for num in numbers:
print(num)
else:
print("All numbers have been printed")
Output:
1
2
3
4
5
All numbers have been printed
Nested Loops
Nested loops are loops within loops. They are used when you need to perform a repetitive action for each item in a nested data structure.
Syntax:
for outer_item in outer_sequence:
for inner_item in inner_sequence:
# Code to be executed
Example:
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
for row in matrix:
for num in row:
print(num)
Output:
1
2
3
4
5
6
7
8
9
Loop Control Statements
Loop control statements alter the flow of execution within loops. They help control which iterations are executed and when the loop terminates.
l. break Statement:
The break statement is used to exit a loop prematurely when a certain condition is met.
Syntax:
for element in sequence:
if condition:
break
Example:
numbers = [1, 2, 3, 4, 5]
for num in numbers:
if num == 3:
break
print(num)
Output:
1
2
ll. continue Statement:
The continue statement is used to skip the current iteration and proceed to the next one.
Syntax:
for element in sequence:
if condition:
continue
Example:
numbers = [1, 2, 3, 4, 5]
for num in numbers:
if num == 3:
continue
print(num)
Output:
1
2
4
5
lll. pass Statement:
The pass statement is a placeholder that does nothing. It's often used when a statement is required syntactically but no action is necessary.
Syntax:
for element in sequence:
if condition:
pass
Example:
for i in range(5):
if i % 2 == 0:
pass # This statement does nothing
else:
print(i, "is odd")
Output:
1 is odd
3 is odd
