If statement in C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of an if statement in C?

An if statement lets the program decide to run some code only if a condition is true. It helps the program make choices.

beginner

Write the basic syntax of an if statement in C.

The basic syntax is:

if (condition) {
    // code to run if condition is true
}

beginner

What happens if the condition in an if statement is false?

If the condition is false, the code inside the if block is skipped and the program continues after the block.

beginner

How do you add an alternative action if the if condition is false?

You use an else block after the if block:

if (condition) {
    // code if true
} else {
    // code if false
}

intermediate

Can you have multiple conditions checked in sequence? How?

Yes, by using else if blocks between if and else to check more conditions one after another.

What does the if statement do in C?

A Repeats code multiple times

B Ends the program

C Defines a new variable

D Runs code only if a condition is true

The if statement runs code only when its condition is true.

Which symbol is used to compare equality in an if condition?

A ==

B =

C !=

D &&

Double equals == checks if two values are equal.

What happens if the if condition is false and there is no else?

A The program crashes

B The code inside <code>if</code> runs anyway

C The code inside <code>if</code> is skipped

D The program asks for input

If the condition is false, the if block is skipped.

How do you check multiple conditions in order?

A Using multiple <code>if</code> statements without <code>else</code>

B Using <code>else if</code> blocks

C Using a <code>switch</code> statement only

D Using a loop

You use else if blocks to check multiple conditions in sequence.

Which of these is a correct if statement in C?

A if (x == 5) { }

B if (x = 5) { }

C if x = 5 { }

D if x == 5 then { }

The correct syntax uses parentheses and double equals: if (x == 5) { }.

Explain how an if statement works in C and write a simple example.

Think about how you decide to do something only if a condition is met.

Describe how to handle two different actions based on a condition using if and else.

Imagine choosing between two paths depending on a yes/no question.

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