Polymorphic Usage

Part of the Object Oriented Programming section of Coddy's C journey — lesson 47 of 61.

Challenge

Easy

Let's prove that polymorphism truly works by writing a function that can process any shape through the base Shape* pointer — whether it's a Circle or a Rectangle.

Building on your existing Circle and Rectangle implementations, you'll add a powerful abstraction: a single function that works with any shape type uniformly.

Your project will include these files:

shape.h: Your base Shape interface with DrawFunc and AreaFunc types.
circle.h and circle.c: Your Circle implementation from the previous lesson.
rectangle.h and rectangle.c: Your Rectangle implementation from the previous lesson.
shape.c: Implement a new function called process_shape that takes a Shape* pointer. This function should call the shape's draw function, then call its area function and print the result with 2 decimal places in the format Area: X.XX.
main.c: Demonstrate polymorphism in action. Read a shape type indicator (c for circle, r for rectangle) followed by the necessary dimensions. Create the appropriate shape, then pass a pointer to its embedded Shape member to process_shape. The same function handles both types!

Your program will receive either:

c followed by a radius value, or
r followed by width and height values

Example output when the inputs are c and 5.0:

Drawing Circle with radius: 5.00
Area: 78.54

Example output when the inputs are r, 4.0, and 3.0:

Drawing Rectangle with width: 4.00 and height: 3.00
Area: 12.00

The magic here is that process_shape has no idea whether it's working with a Circle or Rectangle — it only knows about the Shape interface. By casting your concrete shape's embedded Shape member to a Shape*, you can pass any shape type to this single function. This is polymorphism: one function, multiple behaviors based on the actual object type.

Remember to declare process_shape in shape.h so it can be called from main.c.

Try it yourself

#include <stdio.h>
#include "shape.h"
#include "circle.h"
#include "rectangle.h"

int main() {
    // TODO: Read a char for shape type ('c' for circle, 'r' for rectangle)
    // TODO: If 'c', read radius, create a Circle, and call process_shape with its base
    // TODO: If 'r', read width and height, create a Rectangle, and call process_shape with its base
    return 0;
}