Area of a Rectangle Circle and Trapezium in C

In this C programming algorithm tutorial we are looking at how to implement the mathematical formulas to determine area of a rectangle, circle and trapezium. We will give you the formula, the C source code and the results.

Area of a Rectangle

The mathematical formula to determine the area of a rectangle is:

area = length * width

Let’s look at the implementation in C language of this formula:

#include <stdio.h>

int main() {
	float length,width;
	float area;
	
	printf("Enter the length and width of the rectangle sides: ");
	scanf("%f%f",&length, &width);
	
	area = length * width;
	printf("Area of rectangle is: %.2f\n", area);
	return 0;
}

Example output of the source code will look something like this:

Enter the length and width of the rectangle sides: 2 2
Area of rectangle is: 4.00

Area of a Circle

The mathematical formula to determine the area of a circle is:

area = pi*radius*radius

As you can see we are using the constant PI (π). We are only using 5 decimal digits (that’s enough accuracy for this formula). Of course PI is much larger, for instance here are the first 100 decimal digits of π = 3.14159 26535 89793 23846 26433 83279 50288 41971 69399 37510 58209 74944 59230 78164 06286 20899 86280 34825 34211 70679

#include <stdio.h>

#define PI 3.14159

int main() {
	float radius, area;
	
	printf("Input the radius: ");
	scanf("%f", &radius);
	
	area = PI * radius * radius;
	
	printf("%f\n", area);
	return 0;
}

Output example of the source code:

Input the radius: 12
452.389343

Area of a Trapezium

The mathematical formula to determine the area of a trapezium is:

area = (1/2) * (a + b) * h

Take a look at the implementation of this formula in C language:

#include <stdio.h>

int main() {
	float base1,base2,height;
	float area;
	
	printf("Enter the size of two bases and height of the trapezium: ");
	scanf("%f%f%f",&base1,&base2,&height);
	
	area = 0.5 * ( base1 + base2 ) * height ;
	printf("Area of trapezium is: %.3f\n",area);
	
	return 0;
}

Output example of the source code:

Enter the size of two bases and height of the trapezium: 2 2 3
Area of trapezium is: 6.000

As you can see, these formulas are easy to implement. Also take a look at how to implement formulas to determine the area of different triangles.

That’s all for this tutorial.