Random value in C++

Question

I was practicing a little C++, I created that simple data game exercise, so I came across a problem, how can I generate random values in C and C++?

Taking a look at the site (c plus) I found an example using time as Seed (seed), the problem is after that, I created a code as an example, in it I am creating a class "Data" and creating two methods, the Seed and the "Roll", one will create the seed and generate a value and the other will pass the fixed values and call the Seed, within the main I installed 3 objects of the type Dado and I did the "scrolling", always fall the same values for the 3 objects, are different instances, as in other languages, should not generate different values? This is the goal, create different values for each created data, follow the codes:

data. h

#ifndef DADO_H
#define DADO_H

#include <cstdlib>
#include <ctime>

class Dado
{
public:
    int Seed(int max, int min);
    int Rolar();
};

#endif

cpp.

#include "dado.h"

int Dado::Seed(int max, int min){
   srand(time(NULL));
    return rand() % max + min;
}

int Dado::Rolar(){
    int val_max = 6;
    int val_min = 1;
    return Seed(val_max, val_min);
}

main.cpp

#include <iostream>
#include "dado.h"

using namespace std;

int main()
{
    Dado seed;
    Dado dado_1;
    Dado dado_2;

    cout << "Seed:   " << seed.Seed(6,1) << "\n";
    cout << "Dado_1: " << dado_1.Rolar() << "\n";
    cout << "Dado_2: " << dado_2.Rolar() << "\n";

    return 0;
}

Makefile to help anyone who wants to test

all: main
    rm *.o && ./teste

main: main.o dado.o
    g++ -g -o teste main.o dado.o -Wall

main.o: main.cpp dado.h
    g++ -c -g main.cpp -Wall

dado.o: dado.cpp dado.h
    g++ -c -g dado.cpp -Wall

I also created a demo on ideone with some changes, nothing that changes the result, just to organize the visualization (I don’t use this tool much, so I don’t know if it works with more than one file to do the cpp and header).

Answer 1

The problem is that you’re thinking you should create a new seed every time you actually create the seed just once.

There are still two things that this code is not ideal for. The random generation of C that was used is not very suitable, it is better use the C++. And this class is serving no purpose, the most it could do would be to encapsulate the generation in a simple function. Creating a class for this is to kill bird with a cannon. So I made it as simple as possible. But remember the seed can only be generated once.

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;

int main() {
    srand(time(NULL));
    cout << "Dado_1: " << rand() % 6 + 1 << "\n";
    cout << "Dado_2: " << rand() % 6 + 1 << "\n";
}

Behold working in the ideone. And in the repl it.. Also put on the Github for future reference.