Structure of a C++ program - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple C++ program with main function

What is the output of this C++ program?

C++

#include <iostream>

int main() {
    std::cout << "Hello, C++!" << std::endl;
    return 0;
}

A Hello C++!

B Hello, C++!

C hello, C++!

D Compilation error

💡 Hint

Look carefully at the exact text inside the quotes and the capitalization.

The program prints exactly "Hello, C++!" followed by a newline. The std::endl inserts a newline and flushes the output.

❓ Predict Output

intermediate

Value of variable after execution

What is the value of variable x after running this program?

C++

#include <iostream>

int main() {
    int x = 5;
    x = x + 10;
    std::cout << x << std::endl;
    return 0;
}

A 15

B 10

C 5

D Compilation error

💡 Hint

Look at how x is updated after initialization.

x starts at 5, then 10 is added, so x becomes 15.

❓ Predict Output

advanced

Output of program with missing return in main

What is the output or result of this C++ program?

C++

#include <iostream>

int main() {
    std::cout << "Test";
}

A Test

B Compilation error: missing return statement

C No output

D Runtime error

💡 Hint

In modern C++, main can omit return 0; and still run correctly.

Since C++11, main returns 0 implicitly if no return statement is present. The program prints "Test".

❓ Predict Output

advanced

Output of program with multiple functions

What is the output of this C++ program?

C++

#include <iostream>

void greet() {
    std::cout << "Hi";
}

int main() {
    greet();
    std::cout << " there!" << std::endl;
    return 0;
}

A Compilation error

B

Hi there

C

Hi there!

D !ereht iH

💡 Hint

Check the exact characters printed and the effect of std::endl.

The greet function prints "Hi" without newline. main prints " there!" and then std::endl adds a newline. So output is "Hi there!\n".

🧠 Conceptual

expert

Order of sections in a C++ program

Which of the following shows the correct order of sections in a typical C++ program?

A 1, 3, 2, 4

B 3, 1, 2, 4

C 2, 1, 3, 4

D 1, 2, 3, 4

💡 Hint

Think about what the compiler needs first to understand the program.

First, #include directives bring in libraries. Then namespace declarations set scope. Then functions are declared/defined. Finally, main function runs the program.

Practice

1. Which function does a C++ program start executing from?

easy

A. init()

B. start()

C. begin()

D. main()

Solution

1. Step 1: Understand program entry point

   In C++, the program always starts running from the main() function.

2. Step 2: Identify correct function name

   Other function names like start(), init(), or begin() are not recognized as entry points.

3. Final Answer:

   main() -> Option D

4. Quick Check:

   Program starts at main() [OK]

Hint: Remember: C++ always starts at main() function [OK]

Common Mistakes:

• Thinking start() or init() is the entry point
• Confusing main with other function names
• Assuming program runs from top to bottom without main

2. Which of the following is the correct way to include the input/output library in a C++ program?

easy

A. include <iostream>

B. #include <iostream>

C. #include iostream

D. iostream

Solution

1. Step 1: Recognize correct include syntax

   The correct syntax to include a library is #include <library> with a hash and angle brackets.

2. Step 2: Check each option

   #include <iostream> uses #include <iostream> which is correct. Others miss the hash or angle brackets or use invalid tags.

3. Final Answer:

   #include <iostream> -> Option B

4. Quick Check:

   #include <iostream> is correct [OK]

Hint: Use #include with angle brackets for libraries [OK]

Common Mistakes:

• Omitting the # symbol
• Not using angle brackets around library name
• Using incorrect tags like <include>

3. What will be the output of this C++ program?

#include <iostream>
using namespace std;

int main() {
    cout << "Hello, World!" << endl;
    return 0;
}

medium

A. Hello, World!

B. cout << Hello, World!

C. Hello World

D. Error: missing semicolon

Solution

1. Step 1: Analyze the output statement

   The program uses cout to print the string "Hello, World!" followed by a newline.

2. Step 2: Confirm syntax correctness

   All syntax is correct, so the output will be exactly the string printed.

3. Final Answer:

   Hello, World! -> Option A

4. Quick Check:

   cout prints "Hello, World!" [OK]

Hint: cout prints exactly what is inside quotes [OK]

Common Mistakes:

• Ignoring the comma and exclamation mark
• Confusing cout syntax with printf
• Assuming missing semicolon error

4. Identify the error in this C++ program:

#include <iostream>
using namespace std;

int main() 
    cout << "Hello" << endl;
    return 0;
}

medium

A. Missing semicolon after main()

B. Missing #include directive

C. Missing curly braces { } for main function

D. Incorrect return type for main

Solution

1. Step 1: Check main function syntax

   The main function must have curly braces { } to group its code block.

2. Step 2: Identify missing braces

   The code lacks opening { after main() and closing } at the end, causing syntax error.

3. Final Answer:

   Missing curly braces { } for main function -> Option C

4. Quick Check:

   Main needs { } to group code [OK]

Hint: Always use { } to group main function code [OK]

Common Mistakes:

• Thinking semicolon needed after main()
• Ignoring missing braces error
• Assuming #include is missing

5. You want to write a C++ program that prints "Welcome!" and then ends. Which of these is the correct minimal structure?

hard

A. #include <iostream>
using namespace std;

int main() {
cout << "Welcome!" << endl;
return 0;
}

B. int main() {
cout << "Welcome!" << endl;
}

C. #include <iostream>
int main() {
print("Welcome!");
return 0;
}

D. #include <iostream>
using namespace std;

void main() {
cout << "Welcome!" << endl;
}

Solution

1. Step 1: Check for required includes and namespace

   To use cout, #include <iostream> and using namespace std; are needed.

2. Step 2: Verify main function signature and body

   Main must return int and have curly braces. #include <iostream> using namespace std; int main() { cout << "Welcome!" << endl; return 0; } meets all requirements.

3. Final Answer:

   Option A is the correct minimal structure -> Option A

4. Quick Check:

   Include iostream + main() with return int [OK]

Hint: Include iostream and use int main() with braces [OK]

Common Mistakes:

• Using void main() instead of int main()
• Omitting #include <iostream>
• Using print() instead of cout