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

Recall & Review

beginner

What are function parameters in C++?

Function parameters are variables listed in a function's definition. They act as placeholders for the values (arguments) passed to the function when it is called.

beginner

What is the difference between a parameter and an argument?

A parameter is the variable in the function definition. An argument is the actual value passed to the function when calling it.

beginner

How do you pass parameters by value in C++?

Passing by value means the function gets a copy of the argument. Changes inside the function do not affect the original variable.

intermediate

What does passing parameters by reference mean?

Passing by reference means the function receives the actual variable's address. Changes inside the function affect the original variable.

intermediate

What is a default parameter in a function?

A default parameter has a value assigned in the function declaration. If the caller does not provide an argument, the default value is used.

What happens when you pass a parameter by value to a function?

A The function gets the original variable, so changes affect it.

B The function gets a copy of the argument, so changes inside do not affect the original.

C The function cannot modify the parameter.

D The function receives a pointer to the argument.

Passing by value means the function works with a copy, so the original variable stays unchanged.

How do you declare a function parameter to be passed by reference in C++?

A int &x

B int x

C int *x

D int x = 0

Using & after the type declares a reference parameter, allowing the function to modify the original variable.

What is the purpose of default parameters in functions?

A To force the caller to provide all arguments.

B To prevent the function from modifying arguments.

C To make the function faster.

D To allow the function to have optional arguments with default values.

Default parameters let the caller skip some arguments, using predefined default values instead.

Which of these is a correct function declaration with a default parameter?

A void greet(string name = "Guest");

B void greet(string name);

C void greet(string name = );

D void greet(string = name);

The correct syntax assigns a default value after the parameter type and name.

If a function parameter is declared as int *ptr, how is the argument passed?

A By value

B By reference

C As a pointer to an int variable

D As a constant

int *ptr means the function receives a pointer to an int, allowing indirect access to the variable.

Explain the difference between passing parameters by value and by reference in C++.

Think about whether the function can change the original variable or just a copy.

Describe how default parameters work and why they are useful.

Consider how you can call a function with fewer arguments than parameters.

Practice

1.

What is the purpose of function parameters in C++?

easy

A. To send data into functions so they can use it

B. To define the return type of a function

C. To declare variables inside the function body

D. To specify the function's name

Solution

1. Step 1: Understand function parameters

   Function parameters are variables listed in the function definition that receive values when the function is called.

2. Step 2: Identify their purpose

   They allow the function to work with different data each time it is called, making the function flexible and reusable.

3. Final Answer:

   To send data into functions so they can use it -> Option A

4. Quick Check:

   Function parameters = input data for functions [OK]

Hint: Parameters pass data into functions for reuse [OK]

Common Mistakes:

• Confusing parameters with return types
• Thinking parameters declare variables inside function body
• Believing parameters define function name

2.

Which of the following is the correct syntax to declare a function add that takes two int parameters a and b?

easy

A. int add(int a, int b);

B. int add(a int, b int);

C. int add(int a; int b);

D. int add(int a b);

Solution

1. Step 1: Recall correct parameter syntax

   In C++, parameters are declared as type name pairs separated by commas inside parentheses.

2. Step 2: Check each option

   int add(int a, int b); correctly uses int a, int b. Options A, B, and C have syntax errors like missing comma, wrong order, or semicolon.

3. Final Answer:

   int add(int a, int b); -> Option A

4. Quick Check:

   Parameters = type name, comma separated [OK]

Hint: Parameters need type and name, separated by commas [OK]

Common Mistakes:

• Swapping type and name order
• Using semicolons instead of commas
• Omitting commas between parameters

3.

What will be the output of the following code?

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

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

medium

A. Compilation error

B. Hello, name!

C. Hello, !

D. Hello, Alice!

Solution

1. Step 1: Understand function call with parameter

   The function greet takes a string parameter name and prints "Hello, " plus the value of name.

2. Step 2: Check the argument passed

   In main, greet is called with "Alice", so name becomes "Alice".

3. Final Answer:

   Hello, Alice! -> Option D

4. Quick Check:

   Parameter value replaces variable in output [OK]

Hint: Function prints parameter value passed in call [OK]

Common Mistakes:

• Thinking parameter name prints literally
• Expecting empty output if parameter unused
• Assuming syntax error due to string parameter

4.

Identify the error in this function declaration:

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

medium

A. Parameters should be inside square brackets

B. Missing type for parameter b

C. Function must return int

D. Function name is invalid

Solution

1. Step 1: Check parameter declarations

   Each parameter must have a type and a name. Here, b has no type specified.

2. Step 2: Identify correct syntax

   The correct declaration is void printSum(int a, int b). Missing type causes a syntax error.

3. Final Answer:

   Missing type for parameter b -> Option B

4. Quick Check:

   Every parameter needs a type [OK]

Hint: Each parameter must have a type before its name [OK]

Common Mistakes:

• Omitting type for second or later parameters
• Assuming return type must be int
• Using wrong brackets for parameters

5.

Consider this function that calculates the area of a rectangle:

double area(double width, double height) {
    return width * height;
}

How would you call this function to calculate the area of a rectangle with width 5.0 and height 3.0, and store the result in a variable result?

hard

A. double result = area(width=5.0, height=3.0);

B. double result = area(3.0, 5.0);

C. double result = area(5.0, 3.0);

D. double result = area(5, 3);

Solution

1. Step 1: Understand parameter order and types

   The function expects width first, then height, both as doubles.

2. Step 2: Check each call option

   double result = area(5.0, 3.0); passes 5.0 as width and 3.0 as height correctly. double result = area(3.0, 5.0); swaps them. double result = area(width=5.0, height=3.0); uses invalid named arguments (not supported in C++). double result = area(5, 3); passes ints which convert but less precise.

3. Final Answer:

   double result = area(5.0, 3.0); -> Option C

4. Quick Check:

   Call with correct order and types [OK]

Hint: Match argument order and types exactly [OK]

Common Mistakes:

• Swapping argument order
• Using named arguments (not valid in C++)
• Passing wrong types without conversion