Function calling in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested function calls

What is the output of this C++ code when the main function runs?

C++

#include <iostream>

int add(int a, int b) {
    return a + b;
}

int multiply(int x, int y) {
    return x * y;
}

int main() {
    int result = multiply(add(2, 3), 4);
    std::cout << result << std::endl;
    return 0;
}

A 10

B 24

C 20

D 14

💡 Hint

Remember to evaluate the inner function call first before the outer one.

The add function returns 5 (2 + 3). Then multiply(5, 4) returns 20.

❓ Predict Output

intermediate

Function call with default arguments

What will be printed when this program runs?

C++

#include <iostream>
#include <string>

void greet(std::string name = "Guest") {
    std::cout << "Hello, " << name << "!" << std::endl;
}

int main() {
    greet();
    greet("Alice");
    return 0;
}

A Hello, Alice!\nHello, Guest!

B Hello, !\nHello, Alice!

C Hello, Guest!\nHello, Guest!

D Hello, Guest!\nHello, Alice!

💡 Hint

Check what happens when you call greet() without arguments.

The first call uses the default argument "Guest". The second call uses "Alice".

🔧 Debug

advanced

Identify the error in function call

What error will this code produce when compiled?

C++

#include <iostream>

void printSum(int a, int b) {
    std::cout << a + b << std::endl;
}

int main() {
    printSum(5);
    return 0;
}

A Output: 5

B Compilation error: too few arguments to function 'printSum'

C Runtime error: segmentation fault

D Output: 0

💡 Hint

Check how many arguments the function expects versus how many are given.

printSum requires two int arguments, but only one is provided, causing a compile error.

❓ Predict Output

advanced

Function call with reference parameter

What is the output of this program?

C++

#include <iostream>

void increment(int &num) {
    num += 1;
}

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

A 11

B 10

C Compilation error

D Runtime error

💡 Hint

The function changes the original variable by reference.

The increment function adds 1 to the original variable x by reference, so x becomes 11.

🧠 Conceptual

expert

Understanding function call stack behavior

Consider this code snippet. What is the value of result after main finishes?

C++

#include <iostream>

int factorial(int n) {
    if (n <= 1) return 1;
    return n * factorial(n - 1);
}

int main() {
    int result = factorial(4);
    return 0;
}

A 24

B 10

C 120

D 1

💡 Hint

Recall how factorial is calculated recursively.

factorial(4) = 4 * 3 * 2 * 1 = 24.

Practice

1. What does calling a function in C++ do?

easy

A. Runs the code inside the function

B. Deletes the function

C. Creates a new function

D. Changes the function name

Solution

1. Step 1: Understand what a function call means

   Calling a function means telling the program to run the code inside that function.

2. Step 2: Identify the effect of calling a function

   When called, the function's instructions execute, performing its task.

3. Final Answer:

   Runs the code inside the function -> Option A

4. Quick Check:

   Function call = run function code [OK]

Hint: Function call runs its code block immediately [OK]

Common Mistakes:

• Thinking calling creates or deletes functions
• Confusing function call with function definition
• Assuming function call changes function name

2. Which of the following is the correct way to call a function named printMessage in C++?

easy

A. printMessage();

B. printMessage;

C. call printMessage();

D. function printMessage();

Solution

1. Step 1: Recall the syntax for calling a function

   In C++, to call a function, write its name followed by parentheses and a semicolon.

2. Step 2: Check each option

   printMessage(); uses the correct syntax: printMessage();. Others are incorrect or invalid syntax.

3. Final Answer:

   printMessage(); -> Option A

4. Quick Check:

   Function call syntax = name + () + ; [OK]

Hint: Function calls always end with parentheses and semicolon [OK]

Common Mistakes:

• Omitting parentheses when calling functions
• Adding keywords like 'call' or 'function' incorrectly
• Missing semicolon at the end

3. What is the output of this C++ code?

void greet() {
    std::cout << "Hello!" << std::endl;
}

int main() {
    greet();
    return 0;
}

medium

A. Compilation error

B. greet()

C. No output

D. Hello!

Solution

1. Step 1: Understand what the function greet() does

   The function prints "Hello!" followed by a new line.

2. Step 2: See what main() does

   Main calls greet(), so "Hello!" is printed to the screen.

3. Final Answer:

   Hello! -> Option D

4. Quick Check:

   Function call prints "Hello!" [OK]

Hint: Function call runs its print statements [OK]

Common Mistakes:

• Expecting function name printed instead of output
• Thinking no output because no return value
• Assuming compilation error without syntax issues

4. Identify the error in this code snippet:

void sayHi() {
    std::cout << "Hi!" << std::endl;
}

int main() {
    sayHi;
    return 0;
}

medium

A. Function sayHi is not defined

B. Missing parentheses when calling sayHi

C. Missing semicolon after sayHi

D. Incorrect return type in main

Solution

1. Step 1: Check how sayHi is called

   In main(), sayHi is written without parentheses, so it is not called.

2. Step 2: Understand correct function call syntax

   To call sayHi, it must be sayHi(); with parentheses.

3. Final Answer:

   Missing parentheses when calling sayHi -> Option B

4. Quick Check:

   Function call needs parentheses [OK]

Hint: Always use () to call a function [OK]

Common Mistakes:

• Forgetting parentheses on function calls
• Thinking function name alone calls it
• Ignoring compiler errors about function usage

5. Given this function:

int add(int a, int b) {
    return a + b;
}

What is the correct way to call add to get the sum of 5 and 3 and store it in result?

hard

A. int result = add(5 + 3);

B. int result = add(5);

C. int result = add(5, 3);

D. int result = add();

Solution

1. Step 1: Check the function parameters

   The function add requires two integers as input: a and b.

2. Step 2: Match the call with two arguments

   int result = add(5, 3); passes both 5 and 3 correctly. Others pass wrong number or format of arguments.

3. Final Answer:

   int result = add(5, 3); -> Option C

4. Quick Check:

   Function call needs correct number of arguments [OK]

Hint: Match function parameters count exactly when calling [OK]

Common Mistakes:

• Passing fewer or more arguments than function needs
• Passing expressions without commas for multiple args
• Calling function without any arguments when required