Phase 1 · Day 2 · Learn AI

Comparisons & boolean logic

Conditionals start with expressions that evaluate to True or False. Compare with ==, !=, <, >, <=, and >=.

Combine conditions with and, or, and not. Parentheses help keep complex checks readable.

Comparisons

score = 85
print(score >= 70)   # True
print(score == 100)  # False
print(score != 0)    # True

age = 19
has_id = True
print(age >= 18 and has_id)  # True
print(age < 13 or age > 65)  # False
print(not has_id)            # False

Use == for equality. A single = is assignment and will cause a syntax error inside an if condition.

if / elif / else

An if block runs only when its condition is True. Use elif for more branches and else as the fallback.

Indentation (usually 4 spaces) defines which lines belong to the block. Python has no braces.

Grading with branches

score = int(input("Score (0-100): "))

if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
else:
    grade = "Needs work"

print(f"Grade: {grade}")

Nested checks

temp = 32
raining = True

if temp < 0:
    print("Freezing")
else:
    if raining:
        print("Cold and wet—bring a jacket")
    else:
        print("Cold but dry")

Prefer elif chains over deep nesting when you are picking one outcome from many ranges.

for loops

A for loop walks through each item in a sequence—strings, lists, or a range of numbers.

range(n) gives 0..n-1. range(start, stop) and range(start, stop, step) give finer control.

Looping with range

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

for n in range(1, 6):
    print(f"Square of {n} is {n * n}")

Looping over a list

languages = ["Python", "JavaScript", "Go"]

for lang in languages:
    print(f"I am learning {lang}")

# enumerate gives index + value
for index, lang in enumerate(languages, start=1):
    print(f"{index}. {lang}")

Choose for when you know how many times to repeat, or when you are iterating a known collection.

while loops

A while loop keeps running as long as its condition stays True. You must update something inside the loop or it can run forever.

Use break to exit early and continue to skip to the next iteration.

Countdown with while

count = 3
while count > 0:
    print(count)
    count -= 1
print("Go!")

break and continue

for n in range(1, 10):
    if n == 3:
        continue   # skip 3
    if n == 7:
        break      # stop before printing 7+
    print(n)

If a while loop never ends in Try It, check that the condition eventually becomes False—or add a break.

Practice

Mini challenge: number guessing helper

Ask the user for a secret target (1–10) and a guess. Print "too low", "too high", or "correct" using if/elif/else. Then use a for loop to print all numbers from 1 to the target.

challenge starter

target = int(input("Secret number (1-10): "))
guess = int(input("Your guess: "))

# TODO: compare guess to target with if/elif/else

# TODO: for loop printing 1..target

Interactive

Try It in the browser

Ask for an age as an integer. Print "child" if under 13, "teen" if 13–19, otherwise "adult".

Output

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Errors

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Loops & Conditionals