Summary  
This chapter explains how to define simple functions with parameters and return values, and how to invoke them to organize and reuse code.

General domain of usage  
Mathematical calculations

#define CATCH_CONFIG_MAIN
#include <catch2/catch.hpp>

double calculateTripCost(double distanceKm);

TEST_CASE("Trip cost for 0 km should be $5.0", "[calculateTripCost]") {
    double result = calculateTripCost(0.0);
    REQUIRE(result == Approx(5.0)); // Base fare 5.0 + 0 * 2.0 = 5.0
}

TEST_CASE("Trip cost for 10 km should be $25.0", "[calculateTripCost]") {
    double result = calculateTripCost(10.0);
    REQUIRE(result == Approx(25.0)); // Base fare 5.0 + 10 * 2.0 = 25.0
}

TEST_CASE("Trip cost for 12.5 km should be $30.0", "[calculateTripCost]") {
    double result = calculateTripCost(12.5);
    REQUIRE(result == Approx(30.0)); // Base fare 5.0 + 12.5 * 2.0 = 30.0
}

TEST_CASE("Trip cost for 0.5 km should be $6.0", "[calculateTripCost]") {
    double result = calculateTripCost(0.5);
    REQUIRE(result == Approx(6.0)); // Base fare 5.0 + 0.5 * 2.0 = 6.0
}

TEST_CASE("Trip cost for 100 km should be $205.0", "[calculateTripCost]") {
    double result = calculateTripCost(100.0);
    REQUIRE(result == Approx(205.0)); // Base fare 5.0 + 100 * 2.0 = 205.0
}

TEST_CASE("Trip cost for fractional km 7.75 should be $20.5", "[calculateTripCost]") {
    double result = calculateTripCost(7.75);
    REQUIRE(result == Approx(20.5)); // Base fare 5.0 + 7.75 * 2.0 = 20.5
}

test.cpp

Master the core principles of functions and their practical applications. Learn to declare, use, and optimize functions through topics like parameter handling, scope management, and overloading. Explore recursion, templates, and lambda expressions to build modular, efficient, and reusable code for real-world challenges.

Learn the core ideas of functions, their purpose, creation, and usage, along with how variable scopes influence program logic.

Learn to pass data into functions using value, reference, and pointer arguments. Understand default and constant parameters, and how to handle arrays and custom structures.

Discover how to return data from functions using simple, array, or custom types. Understand when to use the void type for functions with no return value.

Advance your function skills with overloading, recursion, and lambda functions to create more flexible, efficient, and modern code.

Challenge: Simple Function Creation

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