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Generating random integer from a range

I just started learning C++ and I’m trying to generate a random integer thats either 1, 2, or 3. I searched around and all the examples I see of generating random numbers are confusing and always different from the last example I looked at. Is there a simple way to do this?

Answer 1

The modulo solution is the most straightforward but it usually loses randomness as modulo as the tendency to “eat up” the lowest bits of the result.

A more random way is to map [0,1[ over [a,b[ in a linear way:

int roll(int min, int max)
{
   // x is in [0,1[
   double x = rand()/static_cast<double>(RAND_MAX+1); 

   // [0,1[ * (max - min) + min is in [min,max[
   int that = min + static_cast<int>( x * (max - min) );

   return that;
}

A generic version is trivially derived from these to get a roll( T min, T max) version.