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)))