Function prototypes - Mini Project: Build & Apply

Function prototypes

📖 Scenario: You are writing a simple C program that calculates the area of a rectangle. To organize your code better, you will use a function prototype before defining the function.

🎯 Goal: Build a C program that declares a function prototype for calculateArea, defines the function, and uses it to find the area of a rectangle.

📋 What You'll Learn

Create a function prototype for calculateArea that takes two int parameters and returns an int.

Define the function calculateArea after main.

In main, declare two int variables length and width with values 5 and 10 respectively.

Call calculateArea with length and width and store the result in area.

Print the value of area.

💡 Why This Matters

🌍 Real World

Function prototypes are used in C programs to organize code and allow functions to be called before they are defined. This helps in building larger programs with multiple files.

💼 Career

Understanding function prototypes is essential for C programming jobs, embedded systems development, and any role involving low-level programming or performance-critical applications.

1

Create variables for rectangle dimensions

In the main function, declare two int variables called length and width and set them to 5 and 10 respectively.

C

#include 

int main() {
    // Declare length and width variables
    // Your code here

    return 0;
}

Need a hint?

Use int length = 5; and int width = 10; inside main.

2

Add function prototype for calculateArea

Above the main function, write a function prototype for calculateArea that takes two int parameters and returns an int.

C

#include 

// Declare function prototype for calculateArea
// Your code here

int main() {
    int length = 5;
    int width = 10;

    return 0;
}

Need a hint?

Write int calculateArea(int length, int width); before main.

3

Define the calculateArea function

After the main function, define the calculateArea function that takes two int parameters length and width and returns their product.

C

#include 

int calculateArea(int length, int width);

int main() {
    int length = 5;
    int width = 10;

    return 0;
}

// Define calculateArea function
// Your code here

Need a hint?

Define int calculateArea(int length, int width) { return length * width; } after main.

4

Call calculateArea and print the result

Inside main, call calculateArea with length and width, store the result in an int variable called area, and print area using printf.

C

#include 

int calculateArea(int length, int width);

int main() {
    int length = 5;
    int width = 10;

    // Call calculateArea and print the area
    // Your code here

    return 0;
}

int calculateArea(int length, int width) {
    return length * width;
}

Need a hint?

Use int area = calculateArea(length, width); and printf("Area: %d\n", area); inside main.