The conditional statement: if, elif, else and compound conditions

An ATM gives money when the PIN is typed correctly and shows a warning when it is wrong; at a traffic light we cross on green and stop on red. A program must also choose what to do depending on the situation. In a flowchart this is a branch drawn as a rhombus (see “Algorithms and flowcharts” and “Branching algorithms”); in Python it is written with the conditional statement if. Every paper of the 2025–2026 entrance exams had 2–3 tasks on the conditional statement, sometimes including a written program.

Comparisons: when is a condition true?

A condition is an expression whose value is True or False. The simplest conditions are built with comparison operators. Note: equality is written with two equals signs, ==, because a single = is assignment.

Strings are compared character by character, by the codes of the characters — like words in a dictionary: 'apple' < 'apricot' is true because at the third character p comes before r. Capital letters have smaller codes than small letters, so 'Z' < 'a' is also true. Strings of digits are compared character by character too: '10' < '9' is true ('1' < '9'), although 10 > 9. A number is never equal to a string: 5 == '5' → False. Python also allows double inequalities: 10 <= n <= 99 means “n is a two-digit number”.

The value of a condition is an ordinary value: you can print it (print(7 > 3) → True) and store it in a variable: even = n % 2 == 0. Here the comparison n % 2 == 0 is computed first, then True or False is assigned to even; after that if even: is enough. Splitting long conditions into such parts makes a program easier to read.

The full and the incomplete if

Writing rules: a colon (:) follows the condition, and the commands of a branch are written with indentation — usually 4 spaces. Consecutive lines with the same indentation form one block: when the indentation ends, the block ends. else is written at the same indentation as its if. Commands that follow the conditional statement without indentation run in both cases.

n = 38
if n % 5 == 3:
    print(n // 5)
else:
    print(n % 5)
print('end')

7
end

x = 12
y = 5
if x % y == 2:
    y = x * 2
    print(x, y)
    x = y - x
y = y + 1
print(x, y)

12 24
12 25

elif chains and nested conditions

When there are more than two choices, elif (“else if”) is used. Conditions are checked from top to bottom; the branch of the first true condition runs and the rest of the chain is skipped — even if later conditions are also true. If no condition is true, the final else runs (if there is none, nothing happens). That is why the order of the conditions matters: if if n > 10 comes before elif n > 100, the second branch can never run.

s = 'k'
b = 'm'
if s == b:
    print('A')
elif s < b:
    print('B')
elif s == 'k':
    print('C')
else:
    print('D')

B

A branch can contain another conditional statement — this is a nested condition. The inner if is checked only when the outer condition is true. Only the indentation decides which else belongs to which if: an else belongs to the nearest if above it that has the same indentation. Exam programs often nest conditions 2–3 levels deep, so trace them systematically.

1. 1
   Write the starting values

   Copy the variables and their starting values (including the input values) into a table.

2. 2
   Evaluate the condition: ✓ or ✗

   Compute the condition with the current values and write ✓ (true) or ✗ (false) next to it.

3. 3
   If ✗, skip the block

   Skip all lines with a bigger indentation and go to the elif / else at the same indentation or, if there is none, to the line after the block.

4. 4
   If ✓, enter the block

   Carry out the commands, update the variables and repeat steps 2–3 for inner conditions. Once a branch has run, the remaining elif / else parts of that chain are skipped.

5. 5
   Do not forget the commands after it

   The unindented lines after the conditional statement always run — the answer is often produced exactly there.

a = 36
b = 14
if a % b > 5:
    a = a - b
    if a > 2 * b:
        b = b + 3
    else:
        b = b - 3
        if b % 2 == 1:
            a = a + 1
else:
    a = a + b
print(a + b, a - b)

34 12

Compound conditions: and, or, not

Several conditions are joined with logical operators: and is true when both conditions are true; or is true when at least one is true; not reverses the value of a condition. These are the conjunction, disjunction and inversion of the lesson “Boolean logic and logic gates”.

Ready-made patterns for intervals: x lies in [10, 20] — 10 <= x <= 20 (that is, x >= 10 and x <= 20); x lies outside it — x < 10 or x > 20, which is the same as not (10 <= x <= 20). Careful: writing and in the “outside” condition is a mistake — no number is both less than 10 and greater than 20 at the same time, so such a condition is always false.

pairs = [(9, 4), (9, 6), (2, 5), (-1, 3), (8, 8),
         (0, 0), (12, 9), (-5, -5), (7, 1), (10, 11)]
count = 0
for s, t in pairs:
    if s >= 8 and t % 3 != 0 or s < 0:
        count = count + 1
print(count)

5

x = 3
y = 5
if x * y > 15:
    print('#')
elif y ** x != 125:
    print('# #')
else:
    print('# # # #')
if y // x == 1:
    print('# # #')

# # # #
# # #

Remainder conditions and a written task

The exam’s favourite conditions are built on remainders. Learn to recognise them at a glance:

• n % 2 == 0 — n is even; n % 2 == 1 — n is odd;
• n % k == 0 — n is divisible by k; n % k != 0 — it is not;
• n % 10 == 7 — the last digit is 7; n // 10 % 10 == 3 — the tens digit is 3;
• n % 3 == 0 and n % 5 == 0 — n is divisible by 15;
• repeating pattern: if something repeats every k steps, n % k shows where n sits in the pattern.

Let us apply the last idea to a written task. The natural numbers are written into a 4-column table like a “snake”: left to right in odd rows and right to left in even rows.

n = 26
r = n % 8
if r == 0 or r == 1:
    print('A')
elif r == 2 or r == 7:
    print('B')
elif r == 3 or r == 6:
    print('C')
else:
    print('D')

B

A written task needs a complete program: input (int(input())), computation (here the remainder and the conditions) and output (print). DİM does not publish the marking criteria of the written tasks, so write every part clearly and check your program step by step against all cases of the example table and against the “border” values (here numbers with remainder 0, such as 8 and 16).

for t in [10, 33, 50, 1000, 1234]:
    r = t % 60
    colour = '?'
    # choose the colour with if / elif / else
    print(t, colour)

10 green
33 yellow
50 red
1000 red
1234 yellow

for y in [2024, 2100, 2000, 2026]:
    leap = False  # write the condition here
    if leap:
        print(y, 'Yes')
    else:
        print(y, 'No')

2024 Yes
2100 No
2000 Yes
2026 No