If statement in C - Mini Project: Build & Apply

If Statement Basics in C

📖 Scenario: You are creating a simple program to check if a person is old enough to vote. Voting age is 18 years or older.

🎯 Goal: Build a C program that uses an if statement to check a person's age and print whether they can vote or not.

📋 What You'll Learn

Create an integer variable called age with the value 20

Create an integer variable called voting_age with the value 18

Use an if statement to check if age is greater than or equal to voting_age

Print "You can vote!" if the condition is true

Print "You cannot vote yet." if the condition is false

💡 Why This Matters

🌍 Real World

Checking age eligibility is common in many real-world applications like voting, driving, or buying age-restricted products.

💼 Career

Understanding if statements is fundamental for any programming job because it helps make decisions in code.

1

Create the age variable

Create an integer variable called age and set it to 20.

C

#include 

int main() {
    int age = 20;
    // Your code here
    return 0;
}

Hint

Use int age = 20; inside the main function.

2

Create the voting age variable

Create an integer variable called voting_age and set it to 18.

C

#include 

int main() {
    int age = 20;
    int voting_age = 18;
    // Your code here
    return 0;
}

Hint

Use int voting_age = 18; inside the main function after age.

3

Write the if statement to check voting eligibility

Use an if statement to check if age is greater than or equal to voting_age. Inside the if block, write printf("You can vote!\n");. Use an else block to print "You cannot vote yet.\n".

C

#include 

int main() {
    int age = 20;
    int voting_age = 18;

    if (age >= voting_age) {
        // Your code here
    } else {
        // Your code here
    }

    return 0;
}

Hint

Use if (age >= voting_age) and else with printf statements inside each block.

4

Print the result

Run the program and print the output. Use printf statements inside the if and else blocks as before. The program should print You can vote!.

C

#include 

int main() {
    int age = 20;
    int voting_age = 18;

    if (age >= voting_age) {
        printf("You can vote!\n");
    } else {
        printf("You cannot vote yet.\n");
    }

    // Your code here
    return 0;
}

Hint

Compile and run the program to see the output.

Practice

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

easy

A. It stores data in memory.

B. It repeats code multiple times.

C. It runs code only if a condition is true.

D. It defines a new function.

Solution

1. Step 1: Understand the purpose of an if statement

   An if statement checks a condition and decides whether to run the code inside it.

2. Step 2: Compare options with the if statement behavior

   Only It runs code only if a condition is true. correctly describes that the code runs only if the condition is true.

3. Final Answer:

   It runs code only if a condition is true. -> Option C

4. Quick Check:

   If statement = runs code if true [OK]

Hint: If condition true, run code inside braces [OK]

Common Mistakes:

• Confusing if with loops
• Thinking if stores data
• Mixing if with function definition

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

easy

A. if (condition) { printf("Hello"); }

B. if (condition) printf("Hello")

C. if condition: printf("Hello");

D. if condition { printf("Hello"); }

Solution

1. Step 1: Recall correct if statement syntax in C

   The condition must be inside parentheses, and the code block inside braces.

2. Step 2: Check each option

   if (condition) { printf("Hello"); } uses parentheses for condition and braces for code block, which is correct syntax.

3. Final Answer:

   if (condition) { printf("Hello"); } -> Option A

4. Quick Check:

   Parentheses + braces = correct if syntax [OK]

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

Common Mistakes:

• Omitting parentheses around condition
• Using colon instead of braces
• Missing semicolon after printf

3. What will be the output of this code?

int x = 5;
if (x > 3) {
    printf("Yes");
} else {
    printf("No");
}

medium

A. Yes

B. No

C. Error

D. No output

Solution

1. Step 1: Evaluate the condition x > 3

   Since x is 5, 5 > 3 is true.

2. Step 2: Determine which block runs

   The if block runs and prints "Yes" because the condition is true.

3. Final Answer:

   Yes -> Option A

4. Quick Check:

   5 > 3 is true, prints Yes [OK]

Hint: If condition true, prints inside if block [OK]

Common Mistakes:

• Confusing else block execution
• Assuming syntax error without checking code
• Ignoring condition evaluation

4. Find the error in this code snippet:

int a = 10;
if a > 5 {
    printf("Big");
}

medium

A. Variable a is not declared

B. Missing semicolon after printf

C. Braces should be parentheses

D. Condition must be inside parentheses

Solution

1. Step 1: Check if statement syntax

   The condition in an if statement must be inside parentheses in C.

2. Step 2: Identify the error in the code

   The code has if a > 5 { ... } without parentheses around a > 5, which is incorrect.

3. Final Answer:

   Condition must be inside parentheses -> Option D

4. Quick Check:

   Condition needs parentheses [OK]

Hint: Always put condition inside parentheses [OK]

Common Mistakes:

• Using braces instead of parentheses for condition
• Forgetting semicolon after statements
• Assuming variable not declared

5. Consider this code:

int n = 0;
if (n) {
    printf("True");
} else {
    printf("False");
}

What will be printed and why?

hard

A. True, because n is zero

B. False, because zero is false in C

C. Error, n must be boolean

D. No output, program crashes

Solution

1. Step 1: Understand how C treats integers in conditions

   In C, zero means false, any nonzero means true.

2. Step 2: Evaluate the condition if (n)

   Since n is 0, the condition is false, so else block runs.

3. Step 3: Determine output

   The else block prints "False".

4. Final Answer:

   False, because zero is false in C -> Option B

5. Quick Check:

   Zero = false, prints False [OK]

Hint: Zero means false, nonzero means true in if conditions [OK]

Common Mistakes:

• Thinking zero is true
• Expecting boolean type only
• Assuming program error