**Python program to calculate diameter, area and perimeter of a circle** has been given below. Suppose, the radius of a circle is *r* unit, the diameter, area and perimeter of that circle would be (2 * *r*) unit, (*pi* * *r^2*) unit^2 and (2 * *pi* * *r*) unit, respectively. The approximate value of *pi* is 3.141592.

For example, if the radius of a circle is 5 cm, then diameter would be (2 * 5) = 10 cm, area of the circle would be (*pi* * 5^2) = 78.54 cm^2 while perimeter would be (2 * *pi* * *r*) = 31.42 cm.

The algorithm, pseudocode, and time-complexity of the program have also been covered below.

## 1. Algorithm to calculate diameter, area and perimeter of a circle

1. Take the radius *r* of a circle as input.

2. Compute *d = 2 * r*

3. Compute *a = pi * r^2*

4. Compute *p = 2 * pi * r*

5. Declare *d* as the diameter, *a* as the area and *p* as the perimeter of that circle.

## 2. Pseudocode to calculate diameter, area and perimeter of a circle

**Input** : Radius *r* of a circle

**Output** : Diameter *D*, Area *A*, Perimeter *P* of the circle

1. **Procedure** diameterAreaPerimeter(*r*):

2. *D := 2 * r*

3. *A := pi * r^2*

4. *P := 2 * pi * r*

5. **Return** *D, A, P*

6. **End Procedure**

## 3. Time complexity to calculate diameter, area and perimeter of a circle

**Time Complexity: O(1)**

## 4. Python Program & Output to calculate diameter, area and perimeter of a circle

# ************************************** # alphabetacoder.com # Python program to calculate diameter, # area and perimeter of a circle # ************************************** import math # take input r = float(input("Enter the radius of a circle: ")) # calculate diameter d = 2 * r # calculate area a = math.pi * r * r # calculate perimeter p = 2 * math.pi * r # display result upto 3 decimal places print("Diameter: ", round(d, 3)) print("Area: ", round(a, 3)) print("Perimeter: ", round(p, 3))

Output

Enter the radius of a circle: 7

Diameter: 14.0

Area: 153.938

Perimeter: 43.982