Function calling in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a function call in C++?

A function call is when you ask a function to run its code by using its name followed by parentheses, optionally with arguments inside.

beginner

How do you pass information to a function when calling it?

You pass information by putting values called arguments inside the parentheses of the function call.

beginner

What happens if a function returns a value?

When a function returns a value, the function call can be used in expressions or assigned to variables to use that returned value.

beginner

Example: What does this code do?

int add(int a, int b) { return a + b; }
int result = add(3, 4);

It calls the function 'add' with 3 and 4 as arguments. The function adds them and returns 7, which is stored in 'result'.

intermediate

Can a function call be inside another function call?

Yes! This is called nesting. For example, you can call a function inside the arguments of another function call.

What is the correct way to call a function named 'printMessage' with no arguments?

A call printMessage();

B printMessage;

C printMessage();

D printMessage[];

In C++, to call a function you use its name followed by parentheses. If there are no arguments, the parentheses are empty.

If a function 'sum' takes two integers, how do you call it with 5 and 10?

A sum{5, 10};

B sum[5, 10];

C sum 5, 10;

D sum(5, 10);

Function arguments are passed inside parentheses separated by commas.

What does this function call return?

int square(int x) { return x * x; }
square(3);

A 9

B 6

C 3

D 0

The function multiplies 3 by 3 and returns 9.

Which of these is a nested function call?

A sum(2, 3);

B print(sum(2, 3));

C print(); sum(2, 3);

D sum(2, 3); print();

Calling 'sum' inside the arguments of 'print' is nesting function calls.

What happens if you forget the parentheses when calling a function?

A The function does not run; it refers to the function itself.

B The function runs anyway.

C It causes a syntax error.

D The program crashes immediately.

Without parentheses, you refer to the function, not call it.

Explain in your own words what happens when you call a function in C++.

Think about how you ask a friend to do something by name.

Describe how you can use the value returned by a function call.

Returned values are like results you can use immediately.

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