Random numbers in a range and matching pairs

Question

I have to generate a pair of random integers between 1-50. I then need to have my program generate five other numbers with the same range as the two random integers. I know how to generate the first pair but Iam having trouble creating the generation for the other 5. This is C++ by the way.

Answer 1

Assuming that I understand your problem, the following approach works for me.

Note that the 5 numbers will have the same absolute difference given by delta:

int delta = abs(pairOne.x - pairOne.y);

but you didn't mention whether or not x > y or y > x was a constraint (a simple modification can enable this). The code simply finds random numbers with the guaranteed difference (delta) as shown below.

#include <iostream>
#include <random>

struct RandPair {
    int x;
    int y;
};

int main()
{
    // A Mersenne Twister pseudo-random generator:
    typedef std::mt19937 CppRNG;

    // Seed the generator:
    uint32_t seed_val = 0;
    CppRNG RandomGenerator;
    RandomGenerator.seed(seed_val);

    int min = 1;
    int max = 50;

    std::uniform_int_distribution<uint32_t> uniformMinMax(min, max);

    RandPair pairOne;
    RandPair otherPairs[5];

    pairOne.x = uniformMinMax(RandomGenerator);
    pairOne.y = uniformMinMax(RandomGenerator);

    std::cout << pairOne.x << "; " << pairOne.y << std::endl;

    int delta = abs(pairOne.x - pairOne.y);

    int count = 0;
    while (count < 5) {
        int r1 = uniformMinMax(RandomGenerator);
        int r2 = uniformMinMax(RandomGenerator);
        if ( abs(r1 - r2) == delta && count < 5 ) {
            otherPairs[count].x = r1;
            otherPairs[count].y = r2;
            count++;
        }
    }

    for (int i = 0; i<5; i++) {
        std::cout << "delta: " << delta << "; " << otherPairs[i].x << "; " << otherPairs[i].y << std::endl;
    }

    return 0;
}

Answer 2

This solution requires #include <random> and a C++11 capable compiler.

std::random_device rd;
std::mt19937 mt(rd());
std::uniform_int_distribution<int> r1(1, 50);
int first = r1(mt), second = r1(mt);
if (first > second) std::swap(first, second);
std::uniform_int_distribution<int> r2(first, second);
for (int i = 0; i < 5; ++i) {
    std::cout << r2(mt) << '\n';
}

Answer 3

int a, b, low, high;

a = rand()%50 + 1;
b = rand()%50 + 1;

low = min(a,b);
high = max(a,b);

int ar[5];
int range = high-low+1;
for(int i=0; i<5; ++i) {
    ar[i] = rand()%(range) + low;
}

Answer 4

Something like this should work:

void printRandomNumbers( int low, int high )
{
    // Seed the random number generator.
    srand( time(0) )

    // Generate 2 random numbers between low and high (inlcusive).
    int a = ( rand() % ( high-low ) ) + ( low + 1 );
    int b = ( rand() % ( high-low ) ) + ( low + 1 );

    // Find a new low and new high.
    if ( a <= b )
    {
        low = a;
        high = b;
    } else {
        high = a;
        low = b;
    }

    printf("The new low is: %d\nThe new high is: %d\n", low, high);

    // Print 5 numbers inside the new range.
    for ( int i = 0; i < 5; i++ )
    {
        printf( "%d\n", rand() % ( high-low ) + ( low + 1 ) );
    }    
}

int main()
{
    printRandomNumbers(0, 100);
}

If you don't want repeating numbers you're going to need to keep track of the output. Simplest way is using a basic c array[].