C++ generating random numbers

Question

My output is 20 random 1's, not between 10 and 1, can anyone explain why this is happening?

#include <iostream>  #include <ctime>  #include <cstdlib>  using namespace std;  int main()  {      srand((unsigned)time(0));      int random_integer;      int lowest=1, highest=10;      int range=(highest-lowest)+1;      for(int index=0; index<20; index++){          random_integer = lowest+int(range*rand()/(RAND_MAX + 1.0));          cout << random_integer << endl;      }  } 

output: 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Answer 1

Because, on your platform, RAND_MAX == INT_MAX.

The expression range*rand() can never take on a value greater than INT_MAX. If the mathematical expression is greater than INT_MAX, then integer overflow reduces it to a number between INT_MIN and INT_MAX. Dividing that by RAND_MAX will always yield zero.

Try this expression:

random_integer = lowest+int(range*(rand()/(RAND_MAX + 1.0)))