Rand Creates the Same Random Number Over and Over Again

rand() always gives same number

I just started learning c++ and I was trying to recreate an erstwhile blackjack program I had made in high school to examination what I have learned in my grade.

Anyway, every fourth dimension i use rand() i get the same numbers every single time I run the program. IE, the first "hand" that is played is always [ vii, eleven ]. How tin can I make information technology so that the generated numbers are random every time?

This lawmaking is not complete for a blackjack program, but I demand to overcome this rand() issue before I motion on to other calculations. It currently compiles and works as is without whatever other issues.

Thank you so much in advance.

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#include <iostream> #include <cstdlib> using namespace std; int main() { int loop1 = 0; int loop2 = 0; char ans; char ans2; cout << endl; cout << "Welcome to black jack!" << endl; cout << "Endeavor to go as close to 21 without going over." << endl; cout << "HIT ways get another card (value), STAY means keep current values and." << endl; cout << "Permit's begin!" << endl << endl; while (loop1 == 0) { int usr_card1 = rand() % 11 + 1; int usr_card2 = rand() % 11 + one; int deal_card1 = rand() % 11 + 1; int deal_card2 = rand() % eleven + i; int usr_total = usr_card1 + usr_card2; int deal_total = deal_card1 + deal_card2; cout << "You accept: [ " << usr_card1 << ", " << usr_card2 << " ]" << endl; while (loop2 == 0) { cout << "Hit or Stay? (H/S): "; cin >> ans; if (ans == 'h' || ans == 'H') { int usr_cardn = rand() % 11 + 1; usr_total = usr_cardn + usr_total; cout << "[ " << usr_cardn << " ]" << endl; continue; } else if (ans == 'south' || ans == 'Southward') pause; else return 0; } cout << usr_total << endl << endl; cout << "Play once again? (Y/Due north): "; cin >> ans2; if (ans2 == 'y' || ans2 == 'Y') go along; else if (ans2 == 'n' || ans2 == 'N') break; } render 0; }

You oasis't seeded the C random number generator by calling Once srand() ;

Add the following line before you enter your while loop:

srand(time(Zilch));

Y'all will likewise need to include the <ctime> header.

I would propose y'all get away from using the C pseudo random number generator and look into the C++ library <random> .

The C standard recommends not using rand/srand if there are improve ways to generate random numbers available.

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You lot need to seed it.

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/* initialize random seed: */ srand (fourth dimension(0));

For example.

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// This program demonstrates random numbers. #include <iostream> #include <cstdlib> // rand and srand #include <ctime> // For the fourth dimension role using namespace std; int main() { // Get the system fourth dimension. unsigned seed = time(0); // Seed the random number generator. srand(seed); // Display three random numbers. cout << rand() << endl; cout << rand() << endl; cout << rand() << endl; return 0; }

This is just an instance of the numerous methods to obtain random value.

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#include <iostream> #include <chrono> //For system_clock #include <random> int main() { // construct a trivial random generator engine from a time-based seed: unsigned seed = std::chrono::system_clock::now().time_since_epoch().count(); std::default_random_engine generator(seed); std::uniform_real_distribution<double> distributionDouble(1.0, 10.0); // Set the numbers for double. std::uniform_int_distribution<int> distributionInteger(1, 10); // Set the numbers for int. std::cout << "some random numbers betwixt 1.0 and 10.0:\north"; for (int i = 0; i < 10; ++i) { std::cout << distributionDouble(generator) << " "; } std::cout << std::endl; std::cout << "some random numbers between 1 and 10: "; for (int i = 0; i < ten; ++i) { std::cout << distributionInteger(generator) << " "; } std::cout << std::endl; render 0; }

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Thanks then much! These were both very helpful!

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Source: http://www.cplusplus.com/forum/beginner/230838/

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