Function parameters in C++ - Mini Project: Build & Apply

Function parameters

📖 Scenario: You are creating a simple calculator program that adds two numbers. You will learn how to use function parameters to pass values into a function.

🎯 Goal: Build a program that defines a function add which takes two numbers as parameters and returns their sum. Then call this function with specific numbers and print the result.

📋 What You'll Learn

Create a function named add that takes two int parameters named a and b

The function add should return the sum of a and b

Call the function add with the numbers 7 and 5

Print the result of the function call

💡 Why This Matters

🌍 Real World

Functions with parameters are used everywhere in programming to reuse code and perform tasks with different inputs, like calculators, games, and apps.

💼 Career

Understanding function parameters is essential for writing clean, reusable code, a key skill for any software developer.

1

Create the add function with parameters

Write a function named add that takes two int parameters called a and b. The function should return an int. Do not write the function body yet.

C++

// Your code here

Hint

Start by writing the function header int add(int a, int b); and a main function.

2

Implement the add function to return the sum

Complete the add function so it returns the sum of the parameters a and b.

C++

int add(int a, int b);

int main() {
    return 0;
}

int add(int a, int b) {
    // Your code here
}

Hint

Use the return statement to send back the sum of a and b.

3

Call the add function with 7 and 5

Inside the main function, call the add function with the arguments 7 and 5. Store the result in an int variable named result.

C++

int add(int a, int b);

int main() {
    // Your code here
    return 0;
}

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

Hint

Use int result = add(7, 5); inside main to call the function and save the sum.

4

Print the result

Add a std::cout statement inside main to print the value of result. Include #include <iostream> at the top of the program.

C++

#include 

int add(int a, int b);

int main() {
    int result = add(7, 5);
    // Your code here
    return 0;
}

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

Hint

Use std::cout << result << std::endl; to print the sum.

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