Else–if ladder in C++ - Step-by-Step Execution

Concept Flow - Else–if ladder

Start

↓

Check condition1

|Yes↓

Execute block1

↓

End

No↓

Check condition2

|Yes↓

Execute block2

↓

End

No↓

Check condition3

|Yes↓

Execute block3

↓

End

No↓

Execute else block

↓

End

The program checks each condition in order. When one condition is true, it runs that block and skips the rest. If none are true, it runs the else block.

Execution Sample

C++

int x = 15;
if (x < 10) {
  std::cout << "Less than 10";
} else if (x < 20) {
  std::cout << "Less than 20";
} else {
  std::cout << "20 or more";
}

Checks x against conditions and prints which range it falls into.

Execution Table

Step	Condition Checked	Condition Result	Branch Taken	Output
1	x < 10	False	No
2	x < 20	True	Yes	Less than 20
3	Else block	Skipped	No
4	End	N/A	Program ends

💡 Condition x < 20 is true, so the corresponding block runs and the ladder ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
x	15	15	15	15

Key Moments - 2 Insights

Why does the program skip checking the else block after a true condition?

Because once a true condition is found (see Step 2 in execution_table), the program runs that block and exits the else-if ladder immediately.

What happens if all conditions are false?

The else block runs (Step 3 would be 'Yes'), providing a default action when no conditions match.

Visual Quiz - 3 Questions

Look at the execution table, what is the output at Step 2?

A Less than 10

B 20 or more

C Less than 20

D No output

💡 Hint

Check the 'Output' column at Step 2 in the execution_table.

At which step does the program stop checking further conditions?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Branch Taken' column to see when a condition is true and the ladder ends.

If x was 25, which step would produce output?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Refer to the conditions and see which block runs when all conditions fail except else.

Concept Snapshot

Else–if ladder syntax:
if (condition1) { ... }
else if (condition2) { ... }
else { ... }

Checks conditions top to bottom.
Runs first true block only.
Else runs if none true.

Full Transcript

This example shows an else-if ladder in C++. The program checks if x is less than 10. If not, it checks if x is less than 20. If that is true, it prints 'Less than 20' and stops checking further. If none of the conditions are true, it runs the else block. Here, x is 15, so the second condition is true and the output is 'Less than 20'.

Practice

1.

What does an else-if ladder do in C++?

easy

A. Skips all conditions and runs the else block always

B. Runs all conditions regardless of their truth

C. Only runs the last condition in the ladder

D. Checks multiple conditions one by one and runs the first true block

Solution

1. Step 1: Understand the purpose of else-if ladder

   An else-if ladder is used to check multiple conditions in order, one after another.

2. Step 2: Identify how conditions are evaluated

   It runs the code block for the first condition that is true and skips the rest.

3. Final Answer:

   Checks multiple conditions one by one and runs the first true block -> Option D

4. Quick Check:

   Else-if ladder = first true condition runs [OK]

Hint: Remember: else-if stops at first true condition [OK]

Common Mistakes:

• Thinking all conditions run
• Believing else always runs
• Confusing else-if with separate ifs

2.

Which of the following is the correct syntax for an else-if ladder in C++?

int x = 10;
if (x < 5) {
  // code A
} _____ (x < 15) {
  // code B
} else {
  // code C
}

easy

A. else if

B. elseif

C. else_if

D. else if()

Solution

1. Step 1: Recall correct else-if syntax in C++

   The correct keyword is else if with a space, no underscores or parentheses after else.

2. Step 2: Check each option

   Options A, B, and C are invalid syntax in C++.

3. Final Answer:

   else if -> Option A

4. Quick Check:

   Correct syntax = else if [OK]

Hint: Use 'else if' with space, no underscores or parentheses [OK]

Common Mistakes:

• Writing 'elseif' as one word
• Using underscores like 'else_if'
• Adding parentheses after else

3.

What will be the output of this C++ code?

int num = 7;
if (num > 10) {
  std::cout << "Greater than 10";
} else if (num > 5) {
  std::cout << "Greater than 5";
} else {
  std::cout << "5 or less";
}

medium

A. Greater than 5

B. 5 or less

C. Greater than 10

D. No output

Solution

1. Step 1: Evaluate first condition (num > 10)

   7 is not greater than 10, so this block is skipped.

2. Step 2: Evaluate second condition (num > 5)

   7 is greater than 5, so this block runs and prints "Greater than 5".

3. Final Answer:

   Greater than 5 -> Option A

4. Quick Check:

   7 > 5 = true, prints "Greater than 5" [OK]

Hint: Check conditions top to bottom, first true runs [OK]

Common Mistakes:

• Choosing first condition output incorrectly
• Ignoring else-if order
• Assuming else runs always

4.

Find the error in this else-if ladder code snippet:

int score = 85;
if (score >= 90) {
  std::cout << "Grade A";
} else if score >= 80 {
  std::cout << "Grade B";
} else {
  std::cout << "Grade C";
}

medium

A. Missing semicolon after std::cout

B. Missing parentheses around condition in else-if

C. Incorrect use of else instead of else-if

D. Using >= instead of >

Solution

1. Step 1: Check syntax of else-if condition

   In C++, conditions must be inside parentheses. The else-if line lacks parentheses.

2. Step 2: Verify other parts

   Semicolons and operators are correct; only parentheses are missing.

3. Final Answer:

   Missing parentheses around condition in else-if -> Option B

4. Quick Check:

   Conditions need parentheses [OK]

Hint: Always put conditions inside parentheses [OK]

Common Mistakes:

• Forgetting parentheses in if/else-if
• Missing semicolons after statements
• Confusing else and else-if syntax

5.

Write an else-if ladder to print the day of the week given an integer day (1 to 7). What will be printed if day = 5?

int day = 5;
if (day == 1) {
  std::cout << "Monday";
} else if (day == 2) {
  std::cout << "Tuesday";
} else if (day == 3) {
  std::cout << "Wednesday";
} else if (day == 4) {
  std::cout << "Thursday";
} else if (day == 5) {
  std::cout << "Friday";
} else if (day == 6) {
  std::cout << "Saturday";
} else if (day == 7) {
  std::cout << "Sunday";
} else {
  std::cout << "Invalid day";
}

hard

A. Thursday

B. Saturday

C. Friday

D. Invalid day

Solution

1. Step 1: Match the value of day with conditions

   day is 5, so the else-if condition day == 5 is true.

2. Step 2: Identify the output for day == 5

   The code prints "Friday" for day 5.

3. Final Answer:

   Friday -> Option C

4. Quick Check:

   day 5 = Friday [OK]

Hint: Match day number to correct else-if condition [OK]

Common Mistakes:

• Mixing up day numbers and names
• Forgetting else block for invalid days
• Using wrong comparison operators