Conditions in code: if–else

If it is raining, you take an umbrella; otherwise, you take sunglasses. In programming, this is called a condition. The program chooses which code to run based on whether a statement is true or false.

if points > 10:
    print "Passed"
else:
    print "Failed"

The condition points > 10 is either true or false. There is no in-between. The computer evaluates the condition and selects the branch that matches the result.

Follow the program with different values:

if age < 7:
    price = 0
elif age < 18:
    price = 50
else:
    price = 100

age = 5 → 0. age = 12 → 50. age = 18 → 100. age = 7 → 50 (7 is not less than 7).

Boundary values are often a source of errors. Always test exactly at the boundary to see which branch is selected.