if, elif and else in Python Class 11: Decision Programs and Output Tracing

Understand if, elif and else in Python: Decision Programs and Output Tracing

if condition:
    statements
elif condition2:
    statements
else:
    statements

x = 15
if x % 3 == 0:
    print("A")
if x % 5 == 0:
    print("B")
else:
    print("C")

marks = int(input("Enter marks: "))
if marks >= 90:
    grade = "A"
elif marks >= 75:
    grade = "B"
elif marks >= 60:
    grade = "C"
else:
    grade = "D"
print("Grade:", grade)

year = int(input("Year: "))
if (year % 400 == 0) or (year % 4 == 0 and year % 100 != 0):
    print("Leap year")
else:
    print("Not a leap year")

if, elif and else in Python: Decision Programs and Output Tracing: key facts

Structure

• •if condition:
• •elif condition:
• •else:
• •Colon and indentation are required

Only one branch of a chain runs.

Relational operators

• •== equal
• •!= not equal
• •< less
• •> greater
• •<= and >= with equality

Result is True or False.

Logical operators

• •not is highest
• •and next
• •or is lowest
• •Brackets override

Use brackets for clarity.

Leap year

Divisible by 400 | or divisible by 4 and not by 100

2000: leap; 1900: not.

How to answer if, elif and else in Python: Decision Programs and Output Tracing questions

1. 1Write the value of each variable before the first if.
2. 2Evaluate the condition and write True or False.
3. 3In an if-elif chain stop at the first True; separate ifs are all tested.
4. 4Write exactly the output including spaces and the order of print statements.
5. 5For input() programs, remember the input is a string; convert with int() before comparing numbers.

if, elif and else in Python: Decision Programs and Output Tracing in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Tricks to remember if, elif and else in Python: Decision Programs and Output Tracing

Short memory aids. Say each one aloud once, then use it on a question the same day.

• One chain, one branch

  In if-elif-else only the first True branch runs.

  Use it when: Chains.

• Divisible by 4 not 100 or by 400

  Leap year rule in one line.

  Use it when: Leap year.

if, elif and else in Python: Decision Programs and Output Tracing: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

x = 7
if x > 5:
    print("big")
elif x > 2:
    print("medium")
else:
    print("small")

x = 15
if x % 3 == 0:
    print("A")
if x % 5 == 0:
    print("B")
else:
    print("C")

x = 15
if x % 3 == 0:
    print("A")
elif x % 5 == 0:
    print("B")
else:
    print("C")

a, b, c = 14, 37, 25
if a >= b and a >= c:
    big = a
elif b >= c:
    big = b
else:
    big = c
print("Largest:", big)

Where students lose marks in if, elif and else in Python: Decision Programs and Output Tracing

The slips examiners see most often, and what to write instead.

• ✗Mistake: Forgetting the colon

  Treating it like English.

  Wrong working

  if x > 5

  Right working

  if x > 5:

  ✓Do this: Every if, elif, else needs a colon.

  Usually costs: 1 mark

• ✗Mistake: Comparing the string from input()

  Not converting.

  Wrong working

  marks = input(); if marks >= 90:

  Right working

  marks = int(input()); if marks >= 90:

  ✓Do this: input() returns a string.

  Usually costs: 1 mark

• ✗Mistake: Using = in a condition

  Confusing assignment and comparison.

  Wrong working

  if x = 5:

  Right working

  if x == 5:

  ✓Do this: == compares; = assigns.

  Usually costs: 1 mark

Practice questions on if, elif and else in Python: Decision Programs and Output Tracing

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQBoard level

   In an if-elif-else chain, how many branches can run in one execution?
   (a) all
   (b) exactly one
   (c) at least two
   (d) none

   Hint

   First True only.

   Answer

   (b) exactly one

2. Q2 · 3 marks · Short answerHarder board level

   What is the output?

   n = -4
   if n > 0:
       print("positive")
   else:
       if n == 0:
           print("zero")
       else:
           print("negative")

   (3 marks)

   Hint

   Nested else.

   Answer

   n > 0 is False, so the else block runs. n == 0 is False, so the inner else runs. Output: negative.

3. Q3 · 4 marks · Short answerHarder board level

   Write a program that reads three sides of a triangle as integers and prints Equilateral, Isosceles or Scalene. Give the output for 5, 5, 5, for 5, 5, 8 and for 3, 4, 5. (4 marks)

   Hint

   Check equal sides.

   Answer

   if a == b == c: print("Equilateral") elif a == b or b == c or a == c: print("Isosceles") else: print("Scalene"). Outputs: Equilateral, Isosceles, Scalene.

4. Q4 · 1 mark · Assertion-reasonHarder board level

   Assertion (A): In Python, the block of an if statement is identified by indentation.
   Reason (R): Python does not use curly brackets to mark a block.
   (a) Both A and R are true, and R is the correct explanation of A.
   (b) Both A and R are true, but R is not the correct explanation of A.
   (c) A is true, but R is false.
   (d) A is false, but R is true.

   Hint

   Python style.

   Answer

   (a) Both A and R are true, and R is the correct explanation of A.

5. Q5 · 5 marks · Short answerHOTS / competency

   Find and correct the errors in this program and give the output for input 70:

   marks = input("Marks: ")
   if marks >= 75
       print("Distinction")
   elif marks >= 40:
   print("Pass")
   else:
       print("Fail")

   (5 marks)

   Hint

   Three faults: type conversion, a missing colon, and indentation.

   Answer

   Three faults: (1) input() must be converted: marks = int(input("Marks: ")); (2) missing colon after the first condition; (3) the print under elif is not indented. Corrected, the input 70 gives: 70 >= 75 False; 70 >= 40 True; output Pass.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Which keyword adds another condition?Show answer

   elif.

2. 2.What marks a block in Python?Show answer

   Indentation.

3. 3.Does elif run if the if is True?Show answer

   No.

4. 4.Leap year rule?Show answer

   Divisible by 400, or by 4 but not by 100.

5. 5.What type does input() return?Show answer

   A string.

if, elif and else in Python: Decision Programs and Output Tracing: frequently asked questions