Loops

• A loop is a block of instruction(s) that repeats multiple times as long as a condition is true.
• The intent of a loop is to re-execute the same lines of code several times in a program

While Loop

• The while loop is used to repeat a section of code an unknown number of times until a specific condition is met

While Loop General Syntax

while condition:
    statement(s)

While Loop Example

• Script

i = 0
while i < 5:
    print("Hello")
    i += 1

• Output

Hello
Hello
Hello
Hello
Hello

For Loop

• Used to iterate over a sequence

General Syntax

for item in sequence:
    statement(s)

Example

• Script

sequence = ["The", "Quick", "Brown", "Fox"]
for item in sequence:
    print(item)

• Output

The
Quick
Brown
Fox

Break statement

• The same break statement is used to exit out of a loop

payment_per_year = 10000
interest_rate = 0.05
current_year = 0
balance = 0
while (current_year <= 100):
    balance += payment_per_year
    interest = balance * interest_rate / 100
    balance += interest
    if (balance >= goal):
        break
    current_year += 1

• The pass statement transfers control to the header of the innermost enclosing loop

while (sum < goal):
    input_number_as_string = input("Enter a number: ")
    input_number_as_integer = int(input_number_as_string)
    if (input_number_as_integer < 0):
        pass
    sum += n # not executed if n < 0

Nested Loops

• Loops defined within loops are called nested loops.

for i in range(3):
    print(i)
    for j in range(5):
        print(j)