C++ Tutorial 13
In this tutorial we explore advanced uses of functions using C++. We’ll cover how to store functions as variables, pass functions into other functions, store functions in a vector and more. Then we’ll solve 2 problems. We’ll receive lists of numbers and then return a list of only the odd values. We’ll then generate random lists of heads and tails and add up how often each occurs. All of the code and a transcript of the video follows below.
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Code & Transcript
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#include <cstdlib> #include <iostream> #include <string> #include <vector> #include <ctime> #include <numeric> #include <cmath> #include <sstream> // 1. Created to store as a variable and to // pass into other functions double MultBy2(double num){ return num * 2; } // 2. Functions can receive other functions // the first double is the return type followed // by the data types for the parameter double DoMath(std::function<double(double)> func, double num){ return func(num); } // 3. You can store functions in a vector double MultBy3(double num){ return num * 3; } // 4. ----- PROBLEM ----- // Checks for odd using modulus bool IsItOdd(int num){ if(num % 2 == 0){ return false; } else { return true; } } // Receives a list and generates a list of odd values // from that list std::vector<int> ChangeList(std::vector<int> list, std::function<bool(int)> func){ std::vector<int> oddList; for(auto i: list){ if(func(i)){ oddList.push_back(i); } } return oddList; } // ----- 4. END OF PROBLEM ----- // ----- 5. PROBLEM ----- // Generates a random list from the possible values supplied std::vector<char> GetHAndTList(std::vector<char> possibleValues, int numberValuesToGenerate){ srand(time(NULL)); std::vector<char> hAndTList; for(int x = 0; x < numberValuesToGenerate; ++x){ int randIndex = rand() % 2; hAndTList.push_back(possibleValues[randIndex]); } return hAndTList; } // Receives a list and sums the number of matching chars int GetNumberOfMatches(std::vector<char> list, char valueToFind){ int numOfMatches = 0; for(char c: list){ if(c == valueToFind){ numOfMatches++; } } return numOfMatches; } // ----- 5. END OF PROBLEM ----- int main() { // 1. You can store functions as variables auto times2 = MultBy2; std::cout << "5 * 2 = " << times2(5) << "\n"; // 2. Pass a function into a function std::cout << "6 * 2 = " << DoMath(times2, 6) << "\n"; // 3. You can store functions in a vector // Create a vector using the function parameters // and then load the functions into the vector std::vector<std::function<double(double)>> funcs (2); funcs[0] = MultBy2; funcs[1] = MultBy3; std::cout << "2 * 10 = " << funcs[0](10) << "\n"; // 4. ----- PROBLEM ----- // Create a function that receives a list and a function // The function passed will return True or False if a list // value is odd. // The surrounding function will return a list of odd // numbers std::vector<int> listOfNums {1,2,3,4,5}; std::vector<int> oddList = ChangeList(listOfNums, IsItOdd); std::cout << "List of Odds\n"; for(auto i: oddList){ std::cout << i << "\n"; } // ----- 4. END OF PROBLEM ----- // ----- 5. PROBLEM ----- // Create a function that creates a random list using // a limited number of values // Create another function that checks for the number // of matches in a list // Create a random list of Hs and Ts and then output // how many of each were generated std::vector<char> possibleValues {'H', 'T'}; std::vector<char> hAndTList = GetHAndTList(possibleValues, 100); std::cout << "Number of Heads : " << GetNumberOfMatches(hAndTList, 'H') << "\n"; std::cout << "Number of Tails : " << GetNumberOfMatches(hAndTList, 'T') << "\n"; // ----- 5. END OF PROBLEM ----- return 0; } |
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