Conditional Statements

The if statement executes a block of code if a specified condition evaluates to true.

if 5 > 1:
    print('Condition holds true')

Use elif (else if) to specify a new conidtion to test if the previous condition was false.

user_name = input('Enter your username: ')
years = int(input('Enter your age: '))

if user_name == 'Alice':
    print("Username recognized.")
elif years == 25:
     print("Age matches the record.")

The else keyword catches anything which isn't caught by the preceding conditions.

final_score = int(input("Enter your score:"))

if final_score > 100:
    print("Score exceeds maximum limit.")
elif final_score >= 90:
    print("Grade: A")
elif final_score >= 80:
    print("Grade: B")
elif final_score >= 60:
    print("Grade: C")
elif final_score >= 40:
    print("Grade: D")
else:
    print("Grade: F - Needs improvement")

While Loops

The while loop executes a set of statements as long as a condition is true.

counter = 1

while counter <= 100:
    print(counter)
    counter += 1

Alternatively, you can use a sentinel variable to control the loop execution.

num = 1
active = True

while active:
    num += 1
    print(num)
    if num >= 100:
        active = False

The break statement terminates the loop completely, and execution moves to the first statement after the loop body.

print(111)
while True:
    print(222)
    print(333)
    break
    print(444)
print(555)

index = 1
while True:
    index += 1
    print(index)
    if index >= 99:
        break

The continue statement skips the current iteration and continues with the next one, re-evaluating the loop condition.

i = 0
while i <= 9:
    i += 1
    if i == 7:
        continue
    print(i)

Python also supports an else block with while loops, which executes if the loop condition becomes false (unless the loop is termianted by break).

x = 0
while x < 5:
    print(x)
    x += 1
else:
    print("Loop finished naturally.")