Python loop

🔹 While Loop

• A while loop runs as long as a condition is true.
• Useful when we don’t know how many times to iterate beforehand.

Syntax:

while condition:
    # code block

✅ Examples:

1. Basic while loop

i = 5
while i < 10:
    print(i)
    i += 1

1. Break Statement

i = 1
while i < 10:
    print(i)
    if i == 5:
        break   # exits loop immediately
    i += 1

1. Continue Statement

i = 0
while i < 10:
    i += 1
    if i == 5:
        continue  # skips printing when i==5
    print(i)

1. Nested while

counter = 1
while counter <= 3:
    newcounter = 1
    while newcounter <= 2:
        print(counter, newcounter)
        newcounter += 1
    counter += 1

🔹 For Loop

• A for loop is used to iterate over a sequence (list, string, range, etc.).

Syntax:

for variable in sequence:
    # code block

✅ Examples:

1. Iterating a list

list1 = ["1", "2", "3"]
for i in list1:
    print(i)

1. Break Statement

names = ["kumar", "raja", "sam", "ram"]
for i in names:
    if i == "sam":
        break
    print(i)

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1. Continue Statement

names = ["kumar", "raja", "sam", "ram"]
for i in names:
    if i == "sam":
        continue
    print(i)

1. Pass Statement

for i in range(5):
    if i == 3:
        pass   # does nothing, placeholder
    print("i =", i)

1. Nested for loop

list1 = ["a", "b"]
list2 = [1, 2]
for i in list1:
    for j in list2:
        print(i, j)

1. Range function

for i in range(1, 11, 2):   # start=1, stop=10, step=2
    print(i)

🔹 Pattern Programs

⭐ Square Pattern

n = 3
i = 1
while i <= n:
    j = 1
    while j <= n:
        print("*", end=" ")
        j += 1
    print()
    i += 1

⭐ Right-angled Triangle

for i in range(1, 6):
    for j in range(i):
        print("*", end="")
    print()

⭐ Pyramid

n = 5
for i in range(1, n + 1):
    print(" " * (n - i) + "* " * i)

⭐ Diamond

n = 5
for i in range(1, n + 1):
    print(" " * (n - i) + "* " * i)
for i in range(n - 1, 0, -1):
    print(" " * (n - i) + "* " * i)

🔹 Useful Programs

1. Reverse a String

a = "sakthi"
b = ""
for i in a:
    b = i + b
print(b)   # 'ihtkas'

1. Remove Duplicates

lst = ['l', 'k', 's', 'l', 'm', 'k', 'm']
unique = []
for i in lst:
    if i not in unique:
        unique.append(i)
print(unique)   # ['l','k','s','m']

1. Find Minimum

numbers = [5, 2, 8, 1, 6]
minimum = numbers[0]
for n in numbers:
    if n < minimum:
        minimum = n
print("Min:", minimum)