c++ - srand not initializing a new output every time -


this question has answer here:

i'm creating program in need output different thing different time. random, outputs same thing, , yes put in srand.

void setcolor() {     srand(time(null));     int col = rand() % 4 + 1;     if (col == 1)     { cout << "white "; }     else if (col == 2)     { cout << "brown "; }     else if (col == 3)     { cout << "black "; }     else if (col == 4)     { cout << "spotted "; } }  int main()  {     (int = 0; <= 5; ++i)     {          setcolor();     } }

srand must called once , not in each loop.

void setcolor() {     int col = rand() % 4 + 1;     if (col == 1)     { cout << "white "; }     else if (col == 2)     { cout << "brown "; }     else if (col == 3)     { cout << "black "; }     else if (col == 4)     { cout << "spotted "; } }  int main()  {     srand(time(null));     (int = 0; <= 5; ++i)     {          setcolor();     } }

it works way because srand initialize "global variable" used rand() function.

time(null) return number of seconds elapsed 1st january 1970. using 5 times same value because of initialisation of "global variable".

however, in c++, not right way use random values. please prefer use random header instead (http://en.cppreference.com/w/cpp/numeric/random) :

#include <iostream> #include <string> #include <map> #include <random>  int main() {     std::random_device rd;     std::map<int, int> hist;     std::uniform_int_distribution<int> dist(0, 9);     (int n = 0; n < 20000; ++n) {         ++hist[dist(rd)]; // note: demo only: performance of many                            // implementations of random_device degrades sharply                           // once entropy pool exhausted. practical use                           // random_device used seed                            // prng such mt19937     }     (auto p : hist) {         std::cout << p.first << " : " << std::string(p.second/100, '*') << '\n';     } }

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