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How do I find the Rand_Max on my system using C++ code? Just a theory question.

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  • Latest Post Latest Post by Dave Sinkula

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Short answer: RAND_MAX is a compile-time macro (in <cstdlib> / <stdlib.h>) that defines the maximum value rand() can return. The 41 you saw came from a single call to rand() — it was one random sample, not the constant maximum. ’s code called rand() and treated that result as the maximum, which explains the confusion.

A few useful facts and checks:

  • The C/C++ standard only requires RAND_MAX >= 32767; the actual value is implementation-defined. Many Windows/MSVC builds use 32767, while common Linux/glibc builds use 2147483647 (2^31−1). Don’t assume a fixed value across platforms.
  • To determine the macro on your system, inspect the header or refer to the RAND_MAX macro directly in code (that’s what pointed toward). The value is fixed by the library, not discovered by sampling rand().

Practical advice:

  • If you need a guaranteed range or more bits of randomness, prefer the C++11 <random> facilities (e.g., std::mt19937 + std::uniform_int_distribution) rather than rand(). They give controllable ranges and much better statistical properties.
  • If you must use rand(), be careful when mapping to other ranges (divide by RAND_MAX+1.0 or use integer scaling techniques to avoid bias) and know that some implementations only provide ~15 useful bits.

Troubleshooting checklist:

  • Confirm you didn’t accidentally use rand() when you meant the macro.
  • Check the header that defines RAND_MAX on your toolchain.
  • Consider switching to <random> for portable, high-quality results.

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Member Avatar for vinochick 
#include <iostream>

using namespace std;

int main()
{	
	double randomMax = 0.0;
	int rand_max = rand();

	//calculate rand_max
	randomMax = 0 + rand_max;

	//display the value of the RAND_MAX constant
	cout << randomMax << endl;


    return 0;
}   //end of main function
Member Avatar for vinochick

The problem is I'm only getting 41 as the number, which I know isn't correct.

Member Avatar for Dave Sinkula 
#include <iostream>
#include <cmath>
using namespace std;

int main()
{
   cout << "RAND_MAX = " << RAND_MAX << "\n";
   return 0;
}
commented: Smart Guy, knows how to use google. +1
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