Control the Flow: Understanding If-Else and Loops in Python

Control flow in Python – if/else statements for making decisions, and for/while loops for repeating work.

If-else statements: making decisions

An if statement runs code only when a condition is true. Otherwise Python skips it or runs the else block instead:

age = 20
if age >= 18:
    print("You are an adult.")
else:
    print("You are not an adult.")

Checks whether age is 18 or over and prints the matching message.

Elif: adding more conditions

When you need more than two paths, use elif (short for else if). Python checks each condition in order and runs the first one that matches:

temperature = 15
if temperature > 30:
    print("It's a hot day.")
elif temperature > 20:
    print("It's a nice day.")
else:
    print("It's cold.")

Prints a message based on which temperature range applies.

Loops: repeating tasks

Writing the same code ten times is tedious. Loops run a block repeatedly. Python has two: for and while.

For loop: iterates over a sequence – a list, tuple, string, or range. Use it when you know how many times you want to loop.

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

Prints 0 through 4. range(5) generates numbers from 0 up to (but not including) 5.

While loop: keeps going as long as a condition is true. Use it when you do not know the count upfront.

count = 0
while count < 5:
    print(count)
    count += 1

Also prints 0 through 4. The loop stops when count reaches 5.

Breaking out of loops

break exits a loop early:

for i in range(10):
    if i == 5:
        break
    print(i)

Prints 0 through 4, then stops when i hits 5.

Continuing a loop

continue skips the rest of the current iteration and moves to the next:

for i in range(10):
    if i % 2 == 0:
        continue
    print(i)

Prints only the odd numbers between 0 and 9.

Nested loops

A loop inside another loop. Handy for grids, tables, or any two-dimensional data:

for i in range(3):
    for j in range(3):
        print(f"({i}, {j})")

Prints coordinate pairs for a 3×3 grid.

Decisions and loops are what make programs useful rather than just a straight line of instructions. Try modifying the examples – change the conditions, adjust the ranges, see what breaks.