# Basic C Exercises

**C program to find diameter, circumference and area of circle**

Write a C program to input radius of a circle from user and find diameter, circumference and area of the circle. How to calculate diameter, circumference and area of a circle whose radius is given by user in C programming. Logic to find diameter, circumference and area of a circle in C.

#### Required knowledge

Data Types in c, Input/Output in C, C Operators, Constants in C#### Properties of circle

Diameter, circumference and area of a circle formula is given by -

D=2r

C=2πr

A= πr^{2}

Where 'r' is radius of the circle.

#### Logic to find diameter, circumference and area of circle

Below is the step by step descriptive logic to find diameter, circumference and area of a circle -

- Input radius of circle from user. Store it in a variable say radius.
- Apply the formulas to calculate diameter, circumference and area. Use diameter = 2 * radius, circumference = 2 * 3.14 * radius and area = 3.14 * radius * radius.
- 3.Print all resultant value diameter, circumference and area.

**Program to find diameter, circumference and area of circle**

/** * C program to calculate diameter, circumference and area of circle */ #include <stdio.h> int main() { float radius, diameter, circumference, area; /* * Input radius of circle from user */ printf("Enter radius of circle: "); scanf("%f", &radius); /* * Calculate diameter, circumference and area */ diameter = 2 * radius; circumference = 2 * 3.14 * radius; area = 3.14 * (radius * radius); /* * Print all results */ printf("Diameter of circle = %.2f units \n", diameter); printf("Circumference of circle = %.2f units \n", circumference); printf("Area of circle = %.2f sq. units ", area); return 0; }

\n is an escape sequence character used to add new line (move to next line).

Important note: The above program contains a constant value 3.14. It is always recommended to use constant variable to represent such constants. The constant PI is already defined in math.h header file with name M_PI.

Let us rewrite the above program using constant value.

**Program to find diameter, circumference and area of circle using PI constant**

/** * C program to calculate diameter, circumference and area of circle */ #include#include // Used for M_PI int main() { float radius, diameter, circumference, area; /* * Input radius of circle from user */ printf("Enter radius of circle: "); scanf("%f", &radius); /* * Calculate diameter, circumference and area of circle */ diameter = 2 * radius; circumference = 2 * M_PI * radius; area = M_PI * (radius * radius); /* * Print all results */ printf("Diameter of circle = %.2f units \n", diameter); printf("Circumference of circle = %.2f units \n", circumference); printf("Area of circle = %.2f sq. units ", area); return 0; }

%.2f is used to print the fractional value up to two decimal places. You can also use %f to print up to default 6 decimal places.

Important note: C doesn't provides any exponential operator. Hence never play with operations like radius ^ 2 to find power or to evaluate exponents.

**Output:**

Enter radius of circle: 10 Diameter of circle = 20.00 units Circumference of circle = 62.79 units Area of circle = 314.00 sq. units