if, if-else, if-else-if Ladder and Nested if in Java with Output Tracing (ICSE Class 9)

Understand if, if-else, if-else-if Ladder and Nested if with Output Tracing

if, if-else, if-else-if Ladder and Nested if with Output Tracing: key facts

if-else

• •if (condition) block1
• •else block2
• •one block runs

Condition in brackets, boolean.

Ladder rule

• •Conditions tested from the top
• •first true block runs
• •rest skipped
• •final else for the remainder

Order the conditions carefully.

Dangling else

else joins the nearest unmatched if | braces change the pairing

Check the indentation against the pairing.

Equality

• •== compares
• •= assigns
• •if (x = 5) is an error for int x

Use == in conditions.

How to answer if, if-else, if-else-if Ladder and Nested if with Output Tracing questions

1. 1Write the value of each variable.
2. 2Test the first condition: if true, run its block and skip the rest of the ladder.
3. 3If false, move to the next else-if or to the final else.
4. 4For nested if statements, test the inner condition only when the outer one is true.
5. 5After the structure ends, continue with the next statement and write the output.

if, if-else, if-else-if Ladder and Nested if with 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, if-else, if-else-if Ladder and Nested if with Output Tracing

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

• First true wins

  In a ladder only the first true block runs.

  Use it when: Ladder tracing.

• Else sticks to the nearest if

  The dangling else binds to the closest unmatched if.

  Use it when: Nested if tracing.

• No semicolon after the if bracket

  if (x > 0); is an empty statement.

  Use it when: Spotting errors.

if, if-else, if-else-if Ladder and Nested if with Output Tracing: solved examples

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

int n = 7;
if (n % 2 == 0)
System.out.println("Even");
System.out.println("Done");

char g;
if (m >= 90) g = 'A';
else if (m >= 75) g = 'B';
else if (m >= 60) g = 'C';
else if (m >= 40) g = 'D';
else g = 'F';

int b = 5, c = 8;
if (a > b)
if (b > c)
System.out.println("X");
else
System.out.println("Y");
System.out.println("Z");

double bill;
if (units <= 100)
bill = units * 2;
else if (units <= 200)
bill = 200 + (units - 100) * 3;
else
bill = 200 + 300 + (units - 200) * 5;
System.out.println(bill);

if (a == b && b == c)
System.out.println("Equilateral");
else if (a == b || b == c || a == c)
System.out.println("Isosceles");
else
System.out.println("Scalene");

Where students lose marks in if, if-else, if-else-if Ladder and Nested if with Output Tracing

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

• ✗Mistake: Semicolon after the condition

  The if line is treated like a statement.

  Wrong working

  if (n > 0); then println always runs

  Right working

  if (n > 0) println(...)

  ✓Do this: No semicolon after the bracket.

  Usually costs: 1 to 2 marks

• ✗Mistake: Single = in a condition

  Assignment and comparison are confused.

  Wrong working

  if (x = 5)

  Right working

  if (x == 5)

  ✓Do this: Use == to compare.

  Usually costs: 1 mark

• ✗Mistake: Wrong order in a ladder

  The broadest test is placed first.

  Wrong working

  if (m >= 40) before if (m >= 90)

  Right working

  test m >= 90 first

  ✓Do this: Strictest condition first.

  Usually costs: 2 marks

Practice questions on if, if-else, if-else-if Ladder and Nested if with 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

   Which is the correct form?
   (a) if (x = 5) (b) if (x == 5) (c) if x == 5 (d) if (x == 5);

   Hint

   The condition is in brackets and has no semicolon.

   Answer

   (b) if (x == 5)

2. Q2 · 2 marks · Very short answerBoard level

   Write an if-else statement to print "Pass" if marks are at least 40, otherwise "Fail".

   Hint

   Use >=.

   Answer

   if (marks >= 40)
   System.out.println("Pass");
   else
   System.out.println("Fail");

3. Q3 · 3 marks · Short answerHarder board level

   Find the output:

   int x = 15;
   if (x > 10)
   {
   x = x - 5;
   if (x % 2 == 0)
   x = x / 2;
   else
   x = x * 3;
   }
   else
   x = 0;
   System.out.println(x);

   Hint

   Work through the outer block first.

   Answer

   5 (x > 10, so x = 10; 10 % 2 == 0, so x = 10 / 2 = 5)

4. Q4 · 3 marks · Short answerHarder board level

   For n = -4 the code below prints Positive. Explain why and correct it.

   if (n > 0);
   System.out.println("Positive");

   Hint

   What does the semicolon do?

   Answer

   The semicolon after the bracket is an empty statement that belongs to the if, so the println is outside it and always runs. Remove the semicolon: if (n > 0) System.out.println("Positive");

5. Q5 · 4 marks · Short answerHOTS / competency

   A ticket costs Rs 0 below age 5, Rs 50 from 5 to 12, Rs 100 from 13 to 59 and Rs 60 from 60 onwards. Write an if-else-if ladder that stores the price in an int variable fare, and give fare for the ages 4, 12, 13 and 60.

   Hint

   Test the smallest range first.

   Answer

   if (age < 5) fare = 0;
   else if (age <= 12) fare = 50;
   else if (age <= 59) fare = 100;
   else fare = 60;
   Fares: age 4 gives 0; age 12 gives 50; age 13 gives 100; age 60 gives 60.

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.How many blocks run in an if-else?Show answer

   Exactly one.

2. 2.What does a final else do in a ladder?Show answer

   It handles every case not matched above.

3. 3.The else belongs to which if?Show answer

   The nearest unmatched if.

4. 4.Which operator compares two values?Show answer

   ==

5. 5.What does if (x > 0); do?Show answer

   The empty statement is the body of the if.

6. 6.What type must a condition have?Show answer

   boolean

if, if-else, if-else-if Ladder and Nested if with Output Tracing: frequently asked questions