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

std::function<int(int)> addToTotal(int& total);

TEST_CASE("Lambda returns correct running total after each call", "[addToTotal]") {
    int total = 0;
    auto adder = addToTotal(total);
    int result1 = adder(5);
    REQUIRE(result1 == 5); // After adding 5, total should be 5
    int result2 = adder(10);
    REQUIRE(result2 == 15); // After adding 10, total should be 15
    int result3 = adder(15);
    REQUIRE(result3 == 30); // After adding 15, total should be 30
    REQUIRE(total == 30);   // The variable total should be 30
}

TEST_CASE("Lambda works with negative numbers", "[addToTotal]") {
    int total = 0;
    auto adder = addToTotal(total);
    int result1 = adder(-3);
    REQUIRE(result1 == -3); // After adding -3, total should be -3
    int result2 = adder(1);
    REQUIRE(result2 == -2); // After adding 1, total should be -2
    int result3 = adder(2);
    REQUIRE(result3 == 0);  // After adding 2, total should be 0
    REQUIRE(total == 0);    // The variable total should be 0
}

TEST_CASE("Multiple lambdas with different totals", "[addToTotal]") {
    int totalA = 0;
    int totalB = 100;
    auto adderA = addToTotal(totalA);
    auto adderB = addToTotal(totalB);
    REQUIRE(adderA(1) == 1);
    REQUIRE(adderA(2) == 3);
    REQUIRE(totalA == 3);
    REQUIRE(adderB(-50) == 50);
    REQUIRE(adderB(10) == 60);
    REQUIRE(totalB == 60);
}

test.cpp

Master the power of modern C++ lambdas — from writing concise inline functions to capturing variables efficiently. Explore how lambdas simplify code structure, enable functional programming patterns, and enhance flexibility when used with STL algorithms. Learn to handle captures, mutable states, and return types with precision. By the end, you’ll be able to use lambdas confidently for cleaner, faster, and more expressive C++ code.

Discover what lambda expressions are, why they were introduced, and how to use their basic syntax and variable capturing.

Explore more sophisticated lambda capabilities, including capture modes, mutability, and explicit return types.

See how lambdas unlock powerful patterns in the C++ Standard Library, especially with algorithms.

Challenge: Running Total with a Lambda

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