**C++ program to calculate area, perimeter and diagonal of a rectangle** has been given below. Suppose, length and breadth of a rectangle are *l* unit, and *b* unit respectively. Then area, perimeter and diagonal of that rectangle would be *l * b* unit^2, *2 * (l + b)* unit and *sqrt(l^2 + b^2)* unit, respectively.

For example, if length is 7 cm and breadth is 3 cm, then area of the rectangle would be 7 * 3 = 21 cm^2 while perimeter and diagonal would be 2 * (7 + 3) = 20 cm and sqrt(7^2 + 3^2) = sqrt(58) = 7.616 cm.

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

## 1. Algorithm to calculate area, perimeter and diagonal of a rectangle

1. Take the length *l* and the breadth *b* of a rectangle as inputs.

2. Compute *a = l * b*

3. Compute *p = 2 * (l + b)*

4. Compute *d = sqrt(l^2 + b^2)*

3. Declare the *a* as the area, *p* as the perimeter and *d* as the diagonal of that rectangle.

## 2. Pseudocode to calculate area, perimeter and diagonal of a rectangle

**Input** : Length *l* and breadth *b* of a rectangle

**Output** : Area *A*, Perimeter *P* and Diagonal *D* of the rectangle

1. **Procedure** areaPerimeterDiagonal(*l, w*):

2. *A := l * b*

3. *P := 2 * (l + b)*

4. *D := sqrt(l^2 + b^2)*

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

6. **End Procedure**

## 3. Time complexity to calculate area, perimeter and diagonal of a rectangle

**Time Complexity: O(1)**

## 4. C++ Program & Output to calculate area, perimeter and diagonal of a rectangle

/************************************* alphabetacoder.com C++ program to calculate the area, perimeter and diameter of a rectangle **************************************/ #include <iostream> #include <cmath> using namespace std; int main() { // declare variables float l, b, a, p, d; // take input cout << "Enter the length of rectangle: "; cin >> l; cout << "Enter the breadth of rectangle: "; cin >> b; // calculate area a = l * b; // calculate perimeter p = 2 * (l + b); // calculate diagonal d = sqrt(l * l + b * b); // display result cout << "Area: " << a << endl; cout << "Perimeter: " << p << endl; cout << "Diagonal: " << d << endl; return 0; }

Output

Enter the length of rectangle: 15

Enter the breadth of rectangle: 10

Area: 150

Perimeter: 50

Diagonal: 18.0278