Function parameters - Mini Project: Build & Apply

Function parameters

📖 Scenario: You are creating a simple calculator program that adds two numbers. You will use a function that takes two numbers as inputs and returns their sum.

🎯 Goal: Build a C program that defines a function with parameters to add two integers and prints the result.

📋 What You'll Learn

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

The add function should return the sum of a and b.

In main, call the add function with the numbers 5 and 7.

Print the result returned by add.

💡 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 how to write and use functions with parameters is a fundamental skill for any software developer or programmer.

1

Create the add function with parameters

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

C

int add(int a, int b);

// Your code here

Hint

Start by writing the function header: int add(int a, int b) and add a placeholder return.

2

Implement the add function body

Inside the add function, write code to return the sum of a and b.

C

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

int main() {
    return 0;
}

Hint

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

3

Call the add function in main

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

C

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

int main() {
    // Your code here
}

Hint

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

4

Print the result

Add a printf statement in main to print the value of result. Use "%d\n" as the format string.

C

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

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

Hint

Use printf("%d\n", result); to show the sum on the screen.

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 declare variables inside the main function

C. To print output on the screen

D. To create loops inside functions

Solution

1. Step 1: Understand function parameters

   Function parameters allow you to pass information into a function so it can use that data.

2. Step 2: Identify the correct purpose

   Creating loops inside functions, declaring variables inside the main function, and printing output on the screen describe other tasks, not the role of parameters.

3. Final Answer:

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

4. Quick Check:

   Function parameters = send data into functions [OK]

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

Common Mistakes:

• Confusing parameters with variables declared inside main
• Thinking parameters print output
• Mixing parameters with loop control

2. Which of the following is the correct way to declare a function with two integer parameters in C?

easy

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

B. void add(int a, b);

C. void add(int a int b);

D. void add(int a, int b);

Solution

1. Step 1: Check parameter syntax

   Parameters must be separated by commas and each must have a type and name.

2. Step 2: Identify correct syntax

   void add(int a, int b); correctly uses commas and types. void add(int a; int b); uses semicolon instead of comma. void add(int a int b); misses comma. void add(int a, b); misses type for second parameter.

3. Final Answer:

   void add(int a, int b); -> Option D

4. Quick Check:

   Parameters need type and comma [OK]

Hint: Separate parameters with commas and specify type for each [OK]

Common Mistakes:

• Using semicolons instead of commas between parameters
• Omitting type for parameters
• Missing commas between parameters

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

void printSum(int x, int y) {
    printf("%d\n", x + y);
}

int main() {
    printSum(3, 4);
    return 0;
}

medium

A. 7

B. 34

C. 0

D. Compilation error

Solution

1. Step 1: Understand function call and parameters

   The function printSum receives 3 and 4 as parameters and adds them.

2. Step 2: Calculate the sum and output

   3 + 4 equals 7, so printf prints 7 followed by a newline.

3. Final Answer:

   7 -> Option A

4. Quick Check:

   3 + 4 = 7 [OK]

Hint: Sum parameters inside function to get output [OK]

Common Mistakes:

• Thinking parameters concatenate as strings
• Expecting zero output without return
• Assuming syntax error due to missing includes

4. Identify the error in this function declaration:

int multiply(int a, b) {
    return a * b;
}

medium

A. Return statement is incorrect

B. Function must return void

C. Missing type for parameter b

D. Function name is invalid

Solution

1. Step 1: Check parameter declarations

   Each parameter must have a type. Here, 'b' lacks a type.

2. Step 2: Confirm other parts are correct

   Return type int and function name are valid. Return statement syntax is correct.

3. Final Answer:

   Missing type for parameter b -> Option C

4. Quick Check:

   Every parameter needs a type [OK]

Hint: Declare type for every parameter explicitly [OK]

Common Mistakes:

• Omitting type for second or later parameters
• Assuming return type must be void
• Misreading return statement as error

5. You want to write a function that swaps two integers using pointers. Which function parameter list is correct?

hard

A. void swap(int &a, int &b)

B. void swap(int *a, int *b)

C. void swap(int a, int b)

D. void swap(int a*, int b*)

Solution

1. Step 1: Understand swapping with pointers

   To swap values in C, you pass pointers to the variables so the function can modify original data.

2. Step 2: Identify correct pointer syntax

   void swap(int *a, int *b) correctly declares two pointer parameters. void swap(int a, int b) passes by value (won't swap original). void swap(int &a, int &b) uses C++ reference syntax (invalid in C). void swap(int a*, int b*) has incorrect pointer syntax.

3. Final Answer:

   void swap(int *a, int *b) -> Option B

4. Quick Check:

   Use pointers to modify original variables [OK]

Hint: Use int * for pointer parameters to modify originals [OK]

Common Mistakes:

• Passing parameters by value when pointers are needed
• Using C++ reference syntax in C
• Incorrect pointer declaration syntax