If statement in C - Step-by-Step Execution

Concept Flow - If statement

Start

↓

Evaluate condition

↓

Condition True?

No→Skip if block

↓

Execute if block

↓

Continue

↓

End

The program checks a condition. If true, it runs the code inside the if block. Otherwise, it skips it and continues.

Execution Sample

C

#include <stdio.h>

int main() {
    int x = 5;
    if (x > 3) {
        printf("x is greater than 3\n");
    }
    return 0;
}

Checks if x is greater than 3 and prints a message if true.

Execution Table

Step	Condition	Result	Branch Taken	Output
1	x > 3	True	Execute if block	x is greater than 3
2	End of if	N/A	Continue

💡 Condition is true, so the if block runs once, then execution continues.

Variable Tracker

Variable	Start	After if	Final
x	5	5	5

Key Moments - 2 Insights

Why does the code inside the if block run only when the condition is true?

Because the if statement checks the condition first (see execution_table step 1). If the condition is true, it runs the block; otherwise, it skips it.

What happens if the condition is false?

The program skips the if block entirely and continues after it, as shown by the 'Skip if block' path in the concept_flow.

Visual Quiz - 3 Questions

Look at the execution table, what is the output at step 1?

A x is less than 3

B No output

C x is greater than 3

D Error

💡 Hint

Check the Output column in execution_table row 1.

At which step does the program decide to skip the if block if the condition is false?

A Step 2

B Step 1

C Before Step 1

D There is no skip step

💡 Hint

Look at the Branch Taken column in execution_table step 1.

If x was 2 instead of 5, what would happen in the execution table?

A Condition would be false and no output

B Program would crash

C Condition would be true and output printed

D Output would be different text

💡 Hint

Refer to the Condition and Output columns in execution_table step 1.

Concept Snapshot

If statement syntax:
if (condition) {
    // code runs if condition is true
}

Checks condition once.
Runs block only if true.
Skips block if false.

Full Transcript

This visual trace shows how an if statement works in C. The program starts and evaluates the condition inside the if. If the condition is true, it executes the code inside the if block, printing a message. If false, it skips the block and continues. The variable x remains unchanged throughout. The execution table shows each step, the condition result, and what branch the program takes. This helps beginners see exactly when and why the if block runs or is skipped.

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