Example: Calculate Dimensions from Perimeter and One Side in C++

// Calculate Dimensions from Perimeter and One Side
#include <iostream>
#include <cmath>
#include <iomanip>

int main() {
    // Step 1: Declare variables
    double perimeter, knownSide, otherSide, diagonal;

    // Step 2: Prompt user for perimeter
    std::cout << "Enter the perimeter of the rectangle: ";
    std::cin >> perimeter;

    // Step 3: Prompt user for one known side
    std::cout << "Enter the length of one known side: ";
    std::cin >> knownSide;

    // Step 4: Check for valid input
    if (perimeter <= 0 || knownSide <= 0) {
        std::cout << "Error: Perimeter and side length must be positive." << std::endl;
        return 1;
    }
    if (knownSide >= (perimeter / 2)) {
        std::cout << "Error: A side length cannot be greater than or equal to half the perimeter." << std::endl;
        return 1;
    }

    // Step 5: Calculate the other side
    // perimeter = 2 * (side1 + side2) => side1 + side2 = perimeter / 2
    // otherSide = (perimeter / 2) - knownSide
    otherSide = (perimeter / 2.0) - knownSide;

    // Step 6: Calculate the diagonal using both sides
    // diagonal = sqrt(knownSide^2 + otherSide^2)
    diagonal = std::sqrt(std::pow(knownSide, 2) + std::pow(otherSide, 2));

    // Step 7: Display the results
    std::cout << std::fixed << std::setprecision(2);
    std::cout << "The other side of the rectangle is: " << otherSide << std::endl;
    std::cout << "The diagonal of the rectangle is: " << diagonal << std::endl;

    return 0;
}