Compute circle perimeter and area

Last update on September 18 2025 12:32:34 (UTC/GMT +8 hours)

Write a C program to compute the perimeter and area of a circle with a given radius.

C programming: Area and circumference of a circle

In geometry, the area enclosed by a circle of radius r is πr2. Here the Greek letter π represents a constant, approximately equal to 3.14159, which is equal to the ratio of the circumference of any circle to its diameter.

The circumference of a circle is the linear distance around its edge.

Pictorial Presentation:

c programming area and perimeter of a circle

Why is the area of a circle of a circle pi times the square of the radius?

C Code:

#include <stdio.h>

int main() {
   int radius;      /* Variable to store the radius of the circle */
   float area, perimeter;    /* Variables to store the area and perimeter of the circle */ 
   radius = 6;      /* Assigning a value to the radius */

   /* Calculating the perimeter of the circle */
   perimeter = 2 * 3.14 * radius;
   printf("Perimeter of the Circle = %f inches\n", perimeter);
	
   /* Calculating the area of the circle */
   area = 3.14 * radius * radius;
   printf("Area of the Circle = %f square inches\n", area);

   return(0);
}

Explanation:

In the exercise above -

The program includes the standard input/output library <stdio.h>.
It declares several variables:

int radius: Represents the circle radius.
float area and float perimeter: Will store the calculated area and perimeter of the circle.

In the "main()" function:

It assigns the value 6 to the 'radius' variable, representing the circle radius.

The program then calculates the circle's perimeter and area:

Perimeter: It uses the formula 2*3.14* radius to calculate the circle perimeter and stores the result in the 'perimeter' variable. Here, 3.14 is an approximation of the mathematical constant π (pi).
Area: It calculates the area using the formula 3.14*radius*radius (π * r^2) and stores the result in the 'area' variable.

Finally, the program uses the "printf()" function to display the calculated values:

It prints the calculated perimeter with a message: "Perimeter of the Circle = [perimeter] inches."
It prints the calculated area with a message: "Area of the Circle = [area] square inches."

The program returns 0 to indicate successful execution.

Sample Output:

Perimeter of the Circle = 37.680000 inches                             
Area of the Circle = 113.040001 square inches

Flowchart:

C Programming Flowchart: Compute the perimeter and area of a rectangle

For more Practice: Solve these Related Problems:

Write a C program to calculate the circumference and area of a circle with a given radius, formatted to 3 decimal places.
Write a C program to compute the radius of a circle when the area is provided, then calculate its circumference.
Write a C program to determine the area and circumference of a circle given its diameter, using appropriate type conversions.
Write a C program to validate user input for a circle's radius and then calculate its area and circumference.

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C Programming Code Editor:

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