C++ - Random Numbers

Overview

Estimated time: 40–60 minutes

Generate reproducible random numbers using engines and distributions. Learn seeding, ranges, and common pitfalls.

Learning Objectives

• Use std::mt19937 and distributions (uniform_int_distribution, uniform_real_distribution).
• Seed properly and reproduce sequences for tests.

Prerequisites

• C++ - Chrono Time & Date

Uniform integers

#include 
#include 
int main(){
  std::mt19937 rng(123); // fixed seed
  std::uniform_int_distribution dist(1,6);
  for(int i=0;i<3;++i) std::cout << dist(rng) << ' ';
}

Uniform reals

#include 
#include 
int main(){
  std::random_device rd; // non-deterministic seed source
  std::mt19937 rng(rd());
  std::uniform_real_distribution dist(0.0, 1.0);
  std::cout << dist(rng) << "\n";
}

Common Pitfalls

• Seeding with time repeatedly in a loop; create one engine and reuse it.
• Using rand()—prefer facilities.

Checks for Understanding

1. How do you get repeatable results?
2. Why avoid std::rand?

Exercises

1. Roll two dice 100 times and compute the distribution of sums.
2. Generate normally distributed numbers and compute mean/stddev.