Else–if ladder in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the number is positive.

C++

#include <iostream>
using namespace std;

int main() {
    int num = 10;
    if (num [1] 0) {
        cout << "Positive number" << endl;
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

A!=

B==

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '>' to check positivity.

Using '<' which checks for negative numbers.

The condition num > 0 checks if the number is positive.

2fill in blank

medium

Complete the else-if ladder to check if a number is negative.

C++

#include <iostream>
using namespace std;

int main() {
    int num = -5;
    if (num > 0) {
        cout << "Positive" << endl;
    } else if (num [1] 0) {
        cout << "Negative" << endl;
    } else {
        cout << "Zero" << endl;
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

A<

B==

C>=

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' which only checks for zero.

Using '>=' which includes zero and positive numbers.

The condition num < 0 checks if the number is negative.

3fill in blank

hard

Fix the error in the else-if ladder condition to correctly check for zero.

C++

#include <iostream>
using namespace std;

int main() {
    int num = 0;
    if (num > 0) {
        cout << "Positive" << endl;
    } else if (num [1] 0) {
        cout << "Zero" << endl;
    } else {
        cout << "Negative" << endl;
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

A==

B<

C>

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '>' which check for negative or positive numbers.

Using '!=' which checks for not equal, not zero.

The condition num == 0 correctly checks if the number is zero.

4fill in blank

hard

Fill both blanks to complete the else-if ladder that prints the number's sign.

C++

#include <iostream>
using namespace std;

int main() {
    int num = -3;
    if (num [1] 0) {
        cout << "Positive" << endl;
    } else if (num [2] 0) {
        cout << "Negative" << endl;
    } else {
        cout << "Zero" << endl;
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

A>

B<

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the operators in the conditions.

Using '==' or '!=' in the first two conditions.

The first condition checks if num > 0 (positive), the second checks if num < 0 (negative).

5fill in blank

hard

Fill all three blanks to create an else-if ladder that prints "Positive", "Negative", or "Zero" based on the number.

C++

#include <iostream>
using namespace std;

int main() {
    int num = 0;
    if (num [1] 0) {
        cout << "Positive" << endl;
    } else if (num [2] 0) {
        cout << "Negative" << endl;
    } else if (num [3] 0) {
        cout << "Zero" << endl;
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

A>

B<

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' for zero check.

Mixing up the order of conditions.

The conditions check if num > 0 (positive), num < 0 (negative), and num == 0 (zero).

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