for循环中的随机数生成器每次都给出相同的数字 [英] Random number generator in a for loop gives same numbers each time

问题描述

该程序应具有非常原始的老虎机功能，可以旋转三个不同的轮子".每个轮子包含一定数量的字符.函数会生成一个随机数，将其分配为每个车轮中的数组位置，然后产生一个与该位置相对应的符号.

This program is supposed to function as a pretty primitive slot machine with three different "wheels" to spin. Each wheels contains a set amount of characters. A function generates a random number to assign as an array position in each wheel, which then yields a symbol corresponding to that position.

我遇到的问题是，在我的for循环的每次迭代中，随机生成的数字都不会改变.因此，对于每个循环，我基本上总是得到"X-X"或"X @-".我搜索了先前提出的问题，并找到了几个相关的问题，但似乎没有一个可以解决我的特殊问题.

The problem I'm having is that the randomly generated number doesn't change through each iteration of my for loop. So I'm basically always getting "X - X" or " X @ -" for every single loop-through. I've searched through previously asked questions and found several related ones, but none seemed to solve my particular problem.

冗长的代码的道歉:

#include <iostream>
#include <string>
#include <cstdlib>
#include <ctime>

using namespace std;

const int WHEEL_POSITIONS = 30;
const char wheelSymbols[WHEEL_POSITIONS + 1] = "-X-X-X-X-X=X=X=X*X*X*X*X@X@X7X";

struct slotMachine
{
    char symbols[WHEEL_POSITIONS + 1];
    int spinPos;
    char spinSymbol;
} wheels[3];

void startWheels(slotMachine []);
void spinWheels(slotMachine []);
void displayResults(slotMachine []);
bool getWinner(slotMachine []);

int main(void)
{
    int spinNum;

    cout << "How many times do you want to spin the wheel? ";
    cin >> spinNum;

    // Calls startWheels function
    startWheels(wheels);

    for (int i = 0; i < spinNum; i++)
    {
        // Calls spinWheels function
        spinWheels(wheels);

        // Calls displayResults function
        displayResults(wheels);

        // Calls function getWinner; if getWinner is true, outputs winning message
        if (getWinner(wheels) == true)
        {
            cout << "Winner! Matched 3 of " << wheels[0].spinSymbol << "." << endl;
        }
    }

    return 0;

}

// Function to initialize each wheel to the characters stored in wheelSymbols[]
void startWheels(slotMachine fwheels[3])
{
    for (int i = 0; i < 3; i++)
    {
        for (int j = 0; j < (WHEEL_POSITIONS + 1); j++)
        {
            fwheels[i].symbols[j] = wheelSymbols[j];
        }
    }
}

// Function to generate a random position in each wheel
void spinWheels(slotMachine fwheels[3])
{
    time_t seed;

    time(&seed);
    srand(seed);

    for (int i = 0; i < 3; i++)
    {
        fwheels[i].spinPos = (rand() % WHEEL_POSITIONS);
    }
}

void displayResults(slotMachine fwheels[3])
{
    for (int i = 0; i < 3; i++)
    {
        fwheels[i].spinSymbol = fwheels[i].symbols[(fwheels[i].spinPos)];
        cout << fwheels[i].spinSymbol;
    }

    cout << endl;
}

bool getWinner(slotMachine fwheels[3])
{
    if ((fwheels[0].spinSymbol == fwheels[1].spinSymbol) && (fwheels[0].spinSymbol == fwheels[2].spinSymbol) && (fwheels[1].spinSymbol == fwheels[2].spinSymbol))
    {
        return true;
    }

    else
    {
        return false;
    }
}

我确定这很简单，但是我找不到它！

I'm sure it's something simple that I'm missing, but I can't quite find it!

推荐答案

每次调用函数 swheelwheels 时，您都在重新播种随机数生成器.

You are re-seeding your random number generator every time you call the function spinwheels.

将这三行移动到 main 函数的顶部.

Move these three lines into the top of your main function.

   time_t seed;

   time(&seed);
   srand(seed);

当我们使用 rand()生成随机数时，实际上是在使用伪随机数生成器(PRNG)，它根据称为 seed 的特定输入生成固定的随机值序列.设置种子时，我们实际上是在重置序列以再次从同一种子开始.

When we generate random numbers using rand(), we are actually using a pseudo-Random Number Generator (PRNG), which generates a fixed sequence of random-looking values based on a particular input called a seed. When we set the seed, we are effectively resetting the the sequence to start at the same seed again.

您可能会认为每次使用 time 都会产生不同的种子，但每次仍然应该给您带来不同的结果，但是在快速的计算机程序中，经过的时间很少，因此每次调用期间种子实际上都不会改变.

You might think that using time would result in a different seed each time, which should still give you a different result each time, but in a fast computer program, so little time has passed that the seed is effectively unchanged during each call.

这就是为什么，正如另一个答案所提到的，您只应在程序中调用一次 srand().

That is why, as the other answer mentions, you should only call srand() once in your program.

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