If statement in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the number is positive.

C++

int number = 5;
if (number [1] 0) {
    std::cout << "Positive" << std::endl;
}

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

A>

B<

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' will check if the number is negative.

Using '==' checks for equality, not positivity.

Using '!=' checks if number is not zero, which includes negatives.

The '>' operator checks if the number is greater than zero, meaning positive.

2fill in blank

medium

Complete the code to print "Even" if the number is divisible by 2.

C++

int number = 4;
if (number [1] 2 == 0) {
    std::cout << "Even" << std::endl;
}

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

A*

B%

C/

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using '/' divides the number but does not check remainder.

Using '*' or '+' are arithmetic operations not related to divisibility.

The modulus operator '%' gives the remainder. If remainder is 0 when divided by 2, number is even.

3fill in blank

hard

Fix the error in the if statement to check if x is not equal to 10.

C++

int x = 7;
if (x [1] 10) {
    std::cout << "Not 10" << std::endl;
}

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

A=

B==

C!=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' causes assignment, not comparison.

Using '==' checks equality, not inequality.

Using '<' checks if less than, not inequality.

The '!=' operator checks if x is not equal to 10. '=' is assignment, not comparison.

4fill in blank

hard

Fill in the blank to print "Adult" if age is 18 or more.

C++

int age = 20;
if (age [1] 18) {
    std::cout << "Adult" << std::endl;
}

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

A<=

B||

C&&

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' checks if age is less than or equal to 18, which is opposite.

Using '&&' or '||' incorrectly changes logic.

The '>=' operator checks if age is greater than or equal to 18.

5fill in blank

hard

Fill all three blanks to print "Teenager" if age is between 13 and 19 inclusive.

C++

int age = 15;
if (age [1] 13 [2] age [3] 19) {
    std::cout << "Teenager" << std::endl;
}

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

A>=

B<=

C&&

D||

Attempts:

3 left

💡 Hint

Common Mistakes

Using '||' instead of '&&' allows ages outside the range.

Swapping '>=' and '<=' changes the logic.

Using '=' instead of comparison operators causes errors.

The condition checks if age is greater or equal to 13 AND less or equal to 19 using '>=' , '&&', and '<=' operators.

Practice

1. What does an if statement do in C++?

easy

A. Defines a new variable

B. Repeats code multiple times

C. Runs code only if a condition is true

D. Ends the program immediately

Solution

1. Step 1: Understand the purpose of if statement

   An if statement checks a condition and runs code only when that condition is true.

2. Step 2: Compare with other options

   Repeating code is done by loops, defining variables is done by declarations, and ending the program is done by return or exit.

3. Final Answer:

   Runs code only if a condition is true -> Option C

4. Quick Check:

   If statement = runs code if true [OK]

Hint: If checks true condition to run code [OK]

Common Mistakes:

• Confusing if with loops
• Thinking if defines variables
• Believing if ends program

2. Which of the following is the correct syntax for an if statement in C++?

easy

A. if condition { cout << "Yes"; }

B. if condition: cout << "Yes";

C. if (condition) cout << "Yes"

D. if (condition) { cout << "Yes"; }

Solution

1. Step 1: Recall correct if syntax

   In C++, the condition must be inside parentheses and the code block inside curly braces.

2. Step 2: Check each option

   if (condition) { cout << "Yes"; } uses parentheses and curly braces correctly. if condition { cout << "Yes"; } misses parentheses. if condition: cout << "Yes"; uses colon which is invalid in C++. if (condition) cout << "Yes" misses curly braces which is allowed only for single statements but here it is incomplete.

3. Final Answer:

   if (condition) { cout << "Yes"; } -> Option D

4. Quick Check:

   Parentheses + braces = correct if syntax [OK]

Hint: Use parentheses for condition and braces for code [OK]

Common Mistakes:

• Missing parentheses
• Using colon instead of braces
• Omitting braces for multiple statements

3. What will be the output of this code?

int x = 10;
if (x > 5) {
  cout << "Hello";
} else {
  cout << "Bye";
}

medium

A. Hello

B. Bye

C. HelloBye

D. No output

Solution

1. Step 1: Evaluate the condition x > 5

   Since x is 10, which is greater than 5, the condition is true.

2. Step 2: Determine which block runs

   Because the condition is true, the code inside the if block runs, printing "Hello".

3. Final Answer:

   Hello -> Option A

4. Quick Check:

   10 > 5 is true, prints Hello [OK]

Hint: Check condition true or false to pick output [OK]

Common Mistakes:

• Confusing else output
• Ignoring condition result
• Assuming both blocks run

4. Find the error in this code snippet:

int a = 3;
if a > 0 {
  cout << "Positive";
}

medium

A. Missing semicolon after if

B. Condition must be inside parentheses

C. Missing curly braces

D. Variable a is not declared

Solution

1. Step 1: Check the if statement syntax

   The condition in an if statement must be inside parentheses.

2. Step 2: Identify the error

   The code writes if a > 0 { without parentheses, which is invalid syntax.

3. Final Answer:

   Condition must be inside parentheses -> Option B

4. Quick Check:

   If condition needs parentheses [OK]

Hint: Always put condition inside parentheses [OK]

Common Mistakes:

• Omitting parentheses
• Thinking semicolon needed after if
• Assuming braces optional always

5. You want to print "Even" if a number is even, and "Odd" if it is odd. Which code correctly uses an if statement to do this?

int num = 7;
// Your code here

hard

A. if (num % 2 == 0) { cout << "Even"; } else { cout << "Odd"; }

B. if (num / 2 == 0) { cout << "Even"; } else { cout << "Odd"; }

C. if (num % 2 = 0) { cout << "Even"; } else { cout << "Odd"; }

D. if (num % 2 != 0) { cout << "Even"; } else { cout << "Odd"; }

Solution

1. Step 1: Understand how to check even numbers

   A number is even if dividing by 2 leaves remainder 0, checked by num % 2 == 0.

2. Step 2: Analyze each option

   if (num % 2 == 0) { cout << "Even"; } else { cout << "Odd"; } correctly uses num % 2 == 0. if (num / 2 == 0) { cout << "Even"; } else { cout << "Odd"; } uses division instead of modulo, which is wrong. if (num % 2 = 0) { cout << "Even"; } else { cout << "Odd"; } uses assignment = instead of comparison ==. if (num % 2 != 0) { cout << "Even"; } else { cout << "Odd"; } reverses the logic.

3. Final Answer:

   if (num % 2 == 0) { cout << "Even"; } else { cout << "Odd"; } -> Option A

4. Quick Check:

   Modulo 2 equals 0 means even [OK]

Hint: Use modulo (%) to check evenness [OK]

Common Mistakes:

• Using division instead of modulo
• Using = instead of ==
• Reversing condition logic