**Example:**

Input radius: 10

Output diameter: 20 units

Output circumference: 62.83 units

Output area: 314.16 sq. units

### Required knowledge

Basic C programming, FunctionBefore moving on to this program also check how to find diameter, circumference and area of a circle without using functions.

### Program to find diameter, circumference and area using functions

/** * C program to find diameter, circumference and area of a circle using functions */ #include <stdio.h> #include <math.h> //Used for constant PI referred as M_PI /* Function declaration */ double diameter(double radius); double circumference(double radius); double area(double radius); int main() { float radius, dia, circ, ar; /* Reads radius of the circle from user */ printf("Enter radius of the circle: "); scanf("%f", &radius); dia = diameter(radius); //Calls diameter function circ = circumference(radius); //Calls circumference function ar = area(radius); //Calls area function printf("Diameter of the circle = %.2f units\n", dia); printf("Circumference of the circle = %.2f units\n", circ); printf("Area of the circle = %.2f sq. units\n", ar); return 0; } /** * Finds the diameter of a circle whose radius is given */ double diameter(double radius) { return (2 * radius); } /** * Finds circumference of the circle whose radius is given */ double circumference(double radius) { return (2 * M_PI * radius); //M_PI = PI = 3.14 ... } /** * Finds area of the circle whose radius is given */ double area(double radius) { return (M_PI * radius * radius); //M_PI = PI = 3.14 ... }

Output

Enter radius of the circle: 10

Diameter of the circle = 20.00 units

Circumference of the circle = 62.83 units

Area of the circle = 314.16 sq. units

Diameter of the circle = 20.00 units

Circumference of the circle = 62.83 units

Area of the circle = 314.16 sq. units

Happy coding ;)

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