C PROGRAMMING PROGRAM • BASICS & INPUT/OUTPUT

Calculate Circle Area and Circumference

Learn how to calculate circle area and circumference using a clear C program.

BeginnerConstantsFloating-point arithmeticGeometry

PROBLEM UNDERSTANDING

Input and expected output

Sample input

Sample output

Area = 78.54
Circumference = 31.42

COMPLETE C PROGRAM

Complete C implementation

#include <stdio.h>

int main(void)
{
    const double pi = 3.141592653589793;
    double radius;

    printf("Enter radius: ");
    scanf("%lf", &radius);
    printf("Area = %.2f\n", pi * radius * radius);
    printf("Circumference = %.2f\n", 2.0 * pi * radius);
    return 0;
}

CURRENT STEP

Select Start to walk through the important lines.

SELECTED LINE

No line selected

EXPECTED OUTPUT FOR THE SAMPLE

Area = 78.54
Circumference = 31.42

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Apply πr² for area and 2πr for circumference.
Display the computed result.

Apply πr² for area and 2πr for circumference.

EFFICIENCY

Time and space complexity

Time complexity

O(1)

Auxiliary space

O(1)

DEBUGGING CHECKLIST

Common mistakes

Check this

Use the correct format specifier for every variable.

Check this

Initialize variables before using their values.

Check this

Check braces, semicolons and input order carefully.

Try it yourself

Practice: Run the program with the sample input, predict its output, and then test one boundary case of your own.