C++ Randomize Different Variables Using a Constructor

Question


Robot::Robot()

fitness = 5;
totalBattery = 5;

int randNum;

int i = 0;
bool valid = true;

srand(time(NULL));

//get robot's position on board and check to see if it is not starting on the wall
while (valid)
{
    position = (rand()+i++) % 196;

    if (position >= 0 && position <= 14)
    { }
    else if ((position % 14) == 0 || (position % 14) == 13)
    { }
    else if (position >= 183 && position <= 195)
    { }
    else 
    {
        valid = false;
        cout << endl << "MY POSITION IS : " << position << endl << endl;    
    }
}

//randomize Robot Genetics
for (int j = 0; j < genes; j++)
{
    for (int k = 0; k < chromosomes; k++)
    {
        //first 4; set N S E W(what the robot looks for in that direction)
        //0 = empty; 1 = battery; 2 = don't care; 3 = wall
        if (k < 4)
        {
          randNum = ((rand()+i++) % 4);
            switch(randNum)
            {
                //Empty Space
                case 0: 
                    DNA[j][k] = " * ";
                    break;

                //Battery
                case 1:
                    DNA[j][k] = " B ";
                    break;

                //Don't Care
                case 2:
                    DNA[j][k] = " D ";
                    break;

                //Wall
                case 3:
                    DNA[j][k] = " W ";
                    break;

                default:
                    cout << "YOUR CODE SCREWED UP IF YOU ARE IN HERE!! " << endl;
            }
        }
        //direction facing; N S E W
        else if (k < 5)
        {
            randNum = ((rand()+i++) % 4);
            switch(randNum)
            {
                case 0: 
                    DNA[j][k] = "N";
                    break;

                case 1:
                    DNA[j][k] = "S";
                    break;

                case 2:
                    DNA[j][k] = "E";
                    break;

                case 3:
                    DNA[j][k] = "W";
                    break;

                default:
                    cout << "YOUR CODE SCREWED UP IF YOU ARE IN HERE!! " << endl;
                    break;

            }
        }
        //step counter in that direction
        else if (k < 6)
        {
            DNA[j][k] = "0";
        }
        //Rotate Right(R); Rotate Left(L); Move in facing Direction(M); Do Nothing (X)
        else
        {
            randNum = ((rand()+i++) % 4);
            switch(randNum)
            {
                case 0: 
                    DNA[j][k] = "X";
                    break;

                case 1:
                    DNA[j][k] = "L";
                    break;

                case 2:
                    DNA[j][k] = "R";
                    break;

                case 3:
                    DNA[j][k] = "M";
                    break;

                default:
                    cout << "YOUR CODE SCREWED UP IF YOU ARE IN HERE!! " << endl;
                    break;

            }
        }
    }   
}

}

I am trying to construct objects of a class, and I need 200 of them. I am using a vector and iterating through a while loop and each time i construct a new instance of the class, the objects come out with the exact same data. How are you supposed to properly use the randomizer function to get different data into variables while constructing objects of a class? I tried doing research, but it just got me to this point, and I'm unsure why this isn't working. Thank You in advanced.

Adding a default case for something impossible is really ridiculous. If somehow you get a value mod 4 to be >3 your computer is broken. It's not a code problem. — tadman, Dec 12 '16 at 20:03
@tadman: It's quite common to protect yourself against future changes in the code that might have unintended consequences. And besides, while the expression `n % 4` (assuming built-in types here) cannot produce a value greater than 3, it can certainly produce a value less than 0. — Benjamin Lindley, Dec 12 '16 at 20:11
@BenjaminLindley It's the worst form of defensive programming. If that's a really bad thing to have happen, `abort()`. — tadman, Dec 13 '16 at 07:27

score 0 · Answer 1 · answered Dec 12 '16 at 20:01

0

Most likely you are producing objects too fast. If the time() method yields the same value each time you call the constructor it will result in the same "random" values.

If you called srand only once on program startup rand() will yield different values for each object.

answered Dec 12 '16 at 20:01

Paul Kertscher

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I assumed if i iterated through an i value, incrementing it by 1, that each time it randomized, the value couldn't be the same. Are you suggesting that i put srand outside of the constructor? – Rwal27 Dec 12 '16 at 20:06
@Rwal27 _"Are you suggesting that i put srand outside of the constructor?"_ As mentioned in the duplicates answer, you should call `srand()` only once when running your program. – πάντα ῥεῖ Dec 12 '16 at 20:08

C++ Randomize Different Variables Using a Constructor

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