If statement in C++ - Mini Project: Build & Apply

If statement

📖 Scenario: You are creating a simple program that checks if a number is positive or not. This is like checking if the temperature outside is above zero degrees to decide if you need a jacket.

🎯 Goal: Build a program that uses an if statement to check if a number is positive and prints a message accordingly.

📋 What You'll Learn

Create an integer variable called number with the value 10

Create a boolean variable called isPositive that will store if the number is positive

Use an if statement to set isPositive to true if number is greater than 0

Print "The number is positive" if isPositive is true

💡 Why This Matters

🌍 Real World

Checking conditions like this helps programs make decisions, such as turning on a heater if the temperature is cold.

💼 Career

Understanding if statements is essential for any programming job because it controls the flow of decisions in software.

1

DATA SETUP: Create the number variable

Create an integer variable called number and set it to 10.

C++

# Your code here

Hint

Use int number = 10; to create the variable.

2

CONFIGURATION: Create the isPositive variable

Create a boolean variable called isPositive and set it to false.

C++

int number = 10;
// Your code here

Hint

Use bool isPositive = false; to create the variable.

3

CORE LOGIC: Use if statement to check positivity

Use an if statement to check if number is greater than 0. Inside the if, set isPositive to true.

C++

int number = 10;
bool isPositive = false;
// Your code here

Hint

Write if (number > 0) { isPositive = true; } to check and update the variable.

4

OUTPUT: Print the result if number is positive

Write a std::cout statement to print "The number is positive" only if isPositive is true.

C++

int number = 10;
bool isPositive = false;
if (number > 0) {
    isPositive = true;
}
// Your code here

Hint

Use if (isPositive) { std::cout << "The number is positive" << std::endl; } to print the message.

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