If statement in C++ - Step-by-Step Execution

Concept Flow - If statement

Start

↓

Evaluate condition

↓

Execute if-block

↓

Continue

↓

Skip if-block

↓

Continue

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

Execution Sample

C++

#include <iostream>
using namespace std;

int main() {
    int x = 5;
    if (x > 3) {
        cout << "x is greater than 3" << endl;
    }
    cout << "Done" << endl;
    return 0;
}

Checks if x is greater than 3, prints a message if true, then prints "Done".

Execution Table

Step	Condition (x > 3)	Result	Branch Taken	Output
1	5 > 3	True	Execute if-block	x is greater than 3
2	N/A	N/A	Continue after if	Done

💡 After executing the if-block, program continues to print "Done" and ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2
x	5	5	5

Key Moments - 2 Insights

Why does the program print "x is greater than 3"?

Because the condition x > 3 is true at step 1, so the if-block runs and prints the message.

What happens if the condition is false?

The program skips the if-block and directly continues to the next statement, as shown in step 2.

Visual Quiz - 3 Questions

Look at the execution table, what is the condition result at step 1?

A False

B True

C Undefined

D Zero

💡 Hint

Check the 'Condition (x > 3)' column at step 1 in the execution table.

At which step does the program print "Done"?

A Step 1

B Before step 1

C Step 2

D Never

💡 Hint

Look at the 'Output' column in the execution table for when "Done" is printed.

If x was 2 instead of 5, what would happen at step 1?

A Condition false, if-block skipped

B Program crashes

C Condition true, if-block runs

D Output prints twice

💡 Hint

Refer to the condition x > 3 and what happens when it is false in the key moments.

Concept Snapshot

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

Checks condition once.
Runs block only if true.
Skips block if false.
Then continues program.

Full Transcript

This visual trace shows how an if statement works in C++. The program starts by evaluating the condition x > 3. Since x is 5, the condition is true, so the code inside the if-block runs and prints "x is greater than 3". Then the program continues and prints "Done". If the condition were false, the if-block would be skipped and only "Done" would print. Variables remain unchanged during this process.

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